> Do many models underperform or not support non-English languages?

Yes they do. However:

1. German is one of the more common languages to train on so more models will support it than say, Bahasa

2. There should still be a reasonable amount of multi-lingual models available. Particularly if you're OK with using proprietary models via API. AFAIK all the frontier embedding and reranking models (non open-source) are multi-lingual