Hebrew, Aramaic, Sanskrit, Zend, Greek, Latin, Gothic, Lithuanian, Old Church Slavonic, Old High German.
Probably not to aim for fluency in all of them, that would be a tall order. I'm primarily interested in exploring the relationships between them, and with English.
Dexkaden, I might try your approach of learning the grammar first, then the vocabulary on that framework. That might well work for me. I have books for learning New Testament Greek but haven't dipped into them much. The structure of Greek seems not dissimilar to that of Latin, as well as much of the vocabulary, it's just the alphabet that's different in parts.
I used to be fluent, or near fluent, in all of French, German, Spanish and Portuguese. Strangely enough, I've been put off these languages and lost fluency in them. They remind me of my school and university days, which is where I learned them and which were times evoking less than happy memories.
I find that when learning, or keeping up fluency in a language, I get bogged down trying to remember idioms, metaphors and the like which are found in all languages. This wastes a lot of time and energy for me and holds me back. Funny that I've found out that trouble with idioms/metaphors can be an AS trait. Anyone else find this to be a problem in foreign languages? I know I'd be far more productive concentrating on grammar and vocabulary (and thus literal meanings).