A caching issue in DNN 5.2.0 leads into special characters like German umlauts, accents etc. being replaced by "?".
Users, who are familiar with Visual Studio may download latest source code from dotnetnuke.codeplex.com and compile for themselves, all others may work around by setting cache duration to 0 in module settings - if they can afford the associated performance decrease.
To speed up this process, I created a SQL Script as a temporary workaround to adjust caching and back.
To enable/disable caching for all module, go to SQL in Host Settings, paste the script into the textbox, check "run as Script" and hit "execute".
To disable caching, use:
INSERT INTO {databaseOwner}{objectQualifier}TabModuleSettings
(TabModuleID,SettingName,SettingValue,CreatedByUserID,CreatedOnDate,LastModifiedByUserID,LastModifiedOnDate)
SELECT TabModuleID, N'SavedCacheTime', CacheTime, 2, GETDATE(), 2, GETDATE()
FROM {databaseOwner}{objectQualifier}TabModules T
WHERE CacheTime > 0
UPDATE {databaseOwner}{objectQualifier}TabModules
SET CacheTime = 0 WHERE CacheTime <> 0
to re-enable caching, execute
UPDATE M
SET M.CacheTime = S.SettingValue
FROM {databaseOwner}{objectQualifier}TabModules M
INNER JOIN {databaseOwner}{objectQualifier}TabModuleSettings S on M.TabModuleID = S.TabModuleID
WHERE S.SettingName = N'SavedCacheTime'
DELETE FROM {databaseOwner}{objectQualifier}TabModuleSettings
WHERE SettingName = N'SavedCacheTime'
HTH