Need advice on Modern Germanic
To be fair, if it was a time travel thing, just having a PHD in Germanic phonology won't cut it. Babel boxes are about knowledge of how to speak the language itself, meaning speaking it without the need of a dictionary. I would imagine a pro-gem 4 would be someone who can hold advanced conversations in the language from memory, and not simply one who knows about the language. Think about a babel box for a user who wants to put in his skill of, say, Spanish. He can know everything about the grammar, conjugation, and phonology, but he knows very few words and can hold the most basic of conversations - that would still be es-1, because he can only speak a little of the language.
I put myself as gem-pro 1 because, despite knowing a lot of the language structure, grammar, and phonology, I only know a small selection of the lexicon and can speak basic phrases and questions from memory. If it was from study, I would put myself as gem-pro 3, to be honest. I'm translating the Bible into Proto-Germanic, but from Wiktionary resources instead of from my head. Does this make me gem-pro 1 or gem-pro 3?
That's what I think Babel boxes are for, anyways.
But other non-language boxes like boxes for coding languages, scripts,... are exactly that : one's knowledge in a field. Nobody can ever be a gem-pro-4 like someone can be a sp-4. But someone can be a gem-pro-4 like someone is lua-4. At least that's how I think about it.
Ideally, our PHD would know not only soundlaw algebras and conjugations, but also have an excellent grasp of Gothic, Old Norse, ...; which would afford him a solid (Proto-)Germanic vocabulary.