There is no such thing as a "repository of translation of kit instructions". But that would be great.
In our downloads sections there are
some translations. But too little compared to the amount of kits produced.
There are several options. Jim already named one or two.
Herky also noted a viable option.
If the kit is printed, you may scan the text, and use an OCR software to make it editable. Then Google translator helps. Google is fairly good, but since it still makes many mistakes in certain technical areas (as noted above by Jim), human translators still have work. That is another option: to pay a translator if you can afford one. But it isn't cheap.
There exists a a glossary of Polish terms related to paper models. It is very useful. Actually I think there are more than one. This is just one of them:
Card Modeling FAQ Appendix: Polish-English Glossary
But what I've found even more useful, is to search in this forum (or in the German or Polish forums too) for previous builds of the kit by other modelers. Sometimes their build photos are far more enlightening than any instruction set.
Kind regards.