They were cleaner than the 19th century industrial cities and the peoples in them.but I doubt that early medieval settlements were so clean and tidy, and the garments of the people so brilliantly white.
The modern stereotype of the Early Middle Ages as an "age of dirt" is far from the truth.
Even if stereotypes about Medieval Christian Europe having negative attitude to cleannes are partially true, the Slavic cities located along the Baltic Coast in the early 12th century were still mostly Pagan, not Christian.
Of course the problem with excrement was the problem of all big Medieval cities - but cities located in seacoast regions had a somehow easier way to deal with them than cities located in inland areas.

Not really. For example the Eastern part of the Western Pomerania (this is area east of the Oder but west of the border of pre-partitions Poland) was Germanized not before the 19th century. Factor which accelerated Germanization of that territory were Prussian government's actions - prohibition of Polish language as language of sermons in churches (including Lutheran churches) and language of lessons in schools.But the bottom line is that by the end of the Medieval period the city of Stettin, and all the territory from the Elbe to the Oder and some way beyond had an ethnic German population, apart from small Slavic-speaking enclaves.
Here is the list of Evangelical parishes in the Eastern part of the Western Pomerania (Stolp, Bütow and Lauenburg in Pommern counties), in which the language of sermons was Polish until 19th century, when the Prussian authorities started to ban Polish language from those Evangelical parishes:
In the Slupsk (Stolp) county Polish-language sermons were in 6 parishes. At first they were prohibited in Stowęcin (1816), then in Rowy (Rowe) - 1830 -, then in Smołdzino (Schmolsin) - 1833. Then in Gardna Wielka (Groß Garde) - 1850, then in Główczyce (Glowitz) - 1855 - and finally in Cecenowo (Zezenow) - 1876 - and in Kluki (Klucken) - 1890.
In the Bytów (Bütow) county Polish was the language of sermons in Pomysk Wielki (Groß Pomeiske), Jasien and Sominy until 1810, in Borzytuchomin (Borntuchen) until 1828, in Tuchom until 1844 and in Bytów (Bütow) itself - until 1859.
In Lębork (Lauenburg in Pommern) county Polish was the language of sermons: in Garczegórze and Nowa Wieś Lęborska until 1775, in Bożepole Wielkie (Groß Boschpol) until 1809, in Lębork itself until 1820, in Bukowina until 1821, in Brzeźno and Dzięcielec until 1825, in Łebunia until 1830, in Gniewino until 1845, in Łeba (Leba) and Sarbsko until 1850, in Janowice and Zwartowo until 1852, in Salino until 1863, in Osieki until 1865 and in Charbrowo (Charbrow) until 1870.
As the result of prohibition of Polish sermons, Kashubian Evangelical population of that area underwent Germanization within several generations from the moment when Polish sermons were banned in their parishes.
The above given data comes from the article "Rola kościoła ewangelickiego w procesie germanizacji ludności kaszubskiej wschodniej części Pomorza Zachodniego w XIX wieku" ("The role of the Evangelical church in the process of Germanization of the Kashubian population of the eastern part of the Western Pomerania in 19th century"), written by professor Zygmunt Szultka, expert of Pomeranian history, Brandenburgian history and Kashubian history.
Slavic nobility (as well as urban elites) underwent Germanization much easier and faster than "common people" and peasants. The ruling classes in general adopt the language of the "conquerors" much faster than other classes of the society. The same happened in the East in case of Polonization - Lithuanian and Ruthenian nobility as well as urban elites became Polonized relatively very fast - on the other hand the majority of rural population as well as poor people from the towns remained Ruthenian-speaking or Lithuanian-speaking for a very long time, if not until the end of the Rzeczpospolita Obojga Narodów in late 18th century.That situation was achieved by two processes:
1. The immigration of German-speaking settlers from the Netherlands and Western Germany.
2. The adoption of German language and culture by the existing Slavic population.
The second process did not only affect the lower strata of the Slavic-speaking population; much of the Slavic nobility retained its lands and lordships, and became part of the German nobility, for example in Mecklenburg and Pomerania.
It is generally very hard to Germanize or Polonize entire native population of a particular area if there is no government-sponsored effort to do so. And there was usually not much of government-sponsored effort to Germanize Slavic population of East German areas until the emergence of absolute & militaristic Monarchies such as Prussia.
In Medieval times Saxon and Brandenburgian nobility did not care what language serfs in their villages spoke.
In general the factor which encouraged governments to carry out forced assimilation of "conquered" populations was the introduction of mass conscription - it was in the best interest of an Absolute and Militaristic state that all soldiers of its army spoke the same language and were emotionally connected with / devoted to their country.
Modern Nationalism emerged roughly in the same time when mass conscription was introduced in Europe.
That is why large part of eastern German territories had numerous Slavic-speaking population as long as until late 18th century and early to mid-19th century, when particularly Prussian government started to be actively interested in Germanizing so far non-German elements of the state's population.
Warmiacy and Mazurzy (immigrants from Poland) and Kashub population in Teutonic Pomerania certainly did not underwent Germanization. Prussian elites and some Prussian common people probably did - but certainly not all Prussians - until the end of the Medieval. But there were many areas with Prussian-speaking majority even in late 16th and early 17th centuries. Germanization processes in Teutonic state were hampered when it was defeated by Poland-Lithuania and became Poland's vassal. Also part of its territory was then incorporated into the Crown of Poland under the name Royal Prussia - Polonization of nobility & proportion of Polish urban population after that started to increase.A similar process occurred in the Monastic State of the Teutonic Order, where Old Prussians who accepted the rule of the Teutonic Order and did not participate in revolts kept their lands and status as freemen, and eventually became fully germanised. The great majority of the population of East Prussia was ethnically German by the end of the Medieval period, consisting of a mixture of immigrants from Germany, germanised Old Prussians, and germanised immigrants from Poland and Lithuania; immigrants from the two latter areas who retained their Slavic and Baltic languages constituted a small minority.
For example in the Teutonic city of Toruń (Thorn) around year 1400 Polish-speaking citizens were around 6.5% of the population of the city center and around 20% of the population of the suburbs. While in the same Toruń (Thorn) but 60 years later - around year 1460 - Polish-speaking citizens were already 27% of the population of the city center and 50% of the population of the suburbs. Later percentage of Poles in Thorn / Toruń continued to increase.
What do you consider as "the end of the Medieval period"? In 15th century (1401 - 1500) only 40% - up to 50% of the total Teutonic State population spoke German as their primary language. And this is the end of the Medieval period.The great majority of the population of East Prussia was ethnically German by the end of the Medieval period,
After the defeat in the Thirteen Years War of 1454 - 1460 the Teutonic State lost some territories which were inhabited mostly by Polish and Kashubian population - the Royal Prussia - which maybe increased the percentage of German-speaking population in what remained Teutonic territory, but Baltic, Prussian-speaking population was still numerous, and there were also Polish colonists in the southern and south-eastern areas of the Teutonic state.
Easternmost areas of the Teutonic State - e.g. Samogitia - were ethnically Baltic too (Samogitian / Lithuanian).
True. That was by the end of the 17th century / in the early 18th century, I would say.All the descendants of the original Old Prussians who had remained in East Prussia had become ethnically German by the 17th Century, when the Old Prussian language died out.
But not all of them became ethnically German - some became ethnically Lithuanian or Polish.
By the way - it is interesting that Old Prussians eventually underwent Germanization, while inhabitants of territories conquered by the Livonian Order did not - and while the old Baltic language of Prussians eventually died out, Baltic languages of native inhabitants of territories of modern Latvia and Estonia did not die out and these nations have their independent states nowadays to the north of Lithuania, despite centuries of foreign rules.
Those who emigrated from the 1970s onward emigrated because of poverty in Poland - exploiting the chance for a better life - rather than because of their supposed adherence to the German ethnicity more than to Polish.Furthermore, almost all the pre-1945 Polish-speaking minority in East Prussia, the so-called Masurians, emigrated to Germany from the 1970s onward, claiming the status of Ethnic German.
Their chance was all about the fact that they could legitimate themselfes with ancestors who had German citizenship before 1939, which means they could get German citizenship in 1970s much easier than other Poles.
Actually the majority of settlers who came to the Teutonic state came from other areas.1. The immigration of German-speaking settlers from the Netherlands and Western Germany.
As I already wrote I have a book with such statistics (but mainly regarding urban population).
For example immigration to the city of Toruń (Thorn) - already mentioned above regarding its population's ethnic structure - in mid-14th century, was from the following territories (territorial structure of the population):
28% - from the countryside of various areas of the Teutonic State
23% - from the Central-Eastern Germany
12% - from Silesia
4% - from Westphalia
2% - from Saxony and Thuringen
2% - from Bohemia and Moravia
remaining 29% - from various Baltic Sea areas, Poland and Holland
Regarding the city of Danzig (Gdańsk) - in period 1364 - 1430 over 11.000 immigrants gained the civic rights in this city, they came from 1129 different villages or smaller towns. In year 1399 the biggest group of immigrants (733 - over 25%) came to Gdańsk / Danzig from various areas of the Teutonic State. Majority of those 733 - 498 - came to Danzig from areas located not farther than 20 - 30 km from the city. The next largest group came to Danzig in 1399 from Westphalia (286 persons) and Saxony (220 persons). Further group came from Pomerania, Mecklenburg and Schleswig-Holstein (in total 279 persons from these 3 areas). Immigrants from the Kingdom of Poland in 1399 numbered 99 persons (3%). From Silesia - 74 persons (2.5%). From Holland - 69 persons (2%).
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As a curiosity let's mention, that the city of Cracow - Poland's capital in the Middle Ages - had even up to 50% German-speaking population in late 13th century, after the Mongol invasion. During the Mongol invasions Cracow was heavily devastated and later it was re-settled largely with colonists / immigrants from overpopulated parts of Germany. However, in 16th century the city of Cracow was once again ethnically nearly 100% Polish - vast majority of German colonists became Polonized during those three centuries from 1250 to 1550.
As I wrote before - nobility & urban population (especially urban elites) get assimilated much easier than peasants.
But peasants were the vast majority of population of all European territories in the Middle Ages.