Personally I don't think having a shirt name Gundogan and not Gündoğan is an issue since that's the fonts we have at hand.I understand what you mean but these letters are found correctly in all leagues in real and in other FIFA versions. In addition, there are similar letters are found correctly in FIFA 14 such as í é ã ö ü ú etc. So, the problem represented in some letters that can be solved like the rest of the letters.
Sometimes a particular font doesn't even have the 'standard' letter version, now that's an issue.
If you reallty need to have Gündoğan on the shirt in every font possible in the game, you can try software like FontForge, open every font, look for all those diacrytics and if they happen to be there, insert them in the right slots. If they aren't there you might try creating them.
But I don't think any of this is either feasible or important enough for the effort it takes.
@HarryBullZak One more thing I wanted to ask you, I saw in your 18-19 mod you had short 1 second vp6 videos acting as bootflow intro/outro skippers. Which software did you use to create/convert vp6 videos? I must have a tried a dozen tools and there's always some error.