The main language of the app was English. The user could change it to German, French, Russian, Chinese, Spanish, etc. But sometimes the translation was not complete. Sometimes some plug-in was not translated. We used string IDs to identify various texts. Sometimes the ID pointed to the translated text, sometimes not, thus English version of that text was used instead.
Also I reported the bug in the visual style to Microsoft. They refused to fix it and said something like "don't do that".