Google-docs – Select words that are not adjacent in Google Docs

Is this possible in Google Docs?

Yes, it is.

With keyboard shortcuts

1. Ctrl+A
2. Ctrl+Shift+, (that's the comma key)

With menu commands

1. Menu Edit → Select all
2. Menu Format → Font size → Decrease font size

One way to have your "dictionary" include spellings from other languages is to translate the document into the language you desire. This will create a copy of the document in the language you choose.

Though this way may produce some weird results, I find that once translated the "spell check" does provide corrections with the translated language, though it will also still correct English spellings.

An example of one weird result I've seen while translating from an English document to a German one had Sprechen sie deutsch translated to Do you speak English. Though, it appears this may have happened because the document had been translated multiple times between languages before translating it back to English, where I added the line which spell check corrected it for German spelling.

Another weird result was the translation failing to separate words causing the "spell check" to flag the word, but it did give the correction in the language it was translated to.

Hope this helps.