Internationalize sponsors

@k1r1ll or @benni you have to add the translations to the pelicanconf.py of each project. (schul-frei.org, teckids.org/teckids.edugit.io) Maybe below SPONSOR_LOGOS and in this format:

SPONSORSTEXTS = { "de": "Danke...", "en": "Thanks...", "fr": "Merci..." }