Creating an central multi-purpose dictionary / database
I would try http://termbases.eu/ a site that was mentioned under Software: Lexicons in Linguist List.

Broadly, what you have described is a lightweight variety of a dictionary writing system, software for developing a lexicon.

If you were translating digital documents, I would recommend translation memory software. Collecting and managing your multilingual context-specific translations is part of what translation memory software does.

Another possibility, if you happen to be comfortable setting up a wiki, is to create a wiki in the manner of Wiktionary.