For example, Latin is used as a source language for scientific terms in many European languages, and English is used as a source for technology-related terms in other languages
In creole studies, you'll hear languages like this described as lexifiers. So for instance, with Haitian Creole — which takes a lot of grammatical features from West African languages, but has a mostly French vocabulary — you can say that French was the the lexifier. The Wikipedia article on relexification gives a few more examples and some citations.
I've never heard the word "lexifier" used to describe non-creole languages. But if you did use the word that way, I suspect you'd be understood. Calling Norman French the "lexifier" for English legal terminology might not be technically correct but I'd know what you were getting at.
I think the general term for these would be "prestige languages". Though the term itself has a wider application, those languages are chosen as sources of technical-term loanwords because of their prestige.