Well since my area of interest includes mostly history of East Central Europe I plan to learn languages of this region, even those I'm not particularly interested in. Just in case I change my signature these language would be:
Hungarian, German, Polish, Sorbian, Romanian, Slovenian, Lithuanian, Latvian, Albanian, Romany, and I'll try to improve my knowledge of Czech, Ruthenian, Macedonian, Bulgarian, Ukrainian, Belarusian and Russian.
I would also like to know languages that were used in these regions in the past: Latin, Koine Greek, Gothic, Old High German, Old Hungarian, Ottoman Turkish, Old Prussian, and improve my knowledge of Old Church Slavonic and Church Slavonic.
But I also would like to learn languages of other cultures I'm interested in: Old Irish, Old French, Old English, Old Norse, Classical Greek, Ancient Egyptian, Coptic, Hittite, Sanskrit.
There are couple of modern languages I would like to learn also, for instance French, Italian, Spanish, Finnish and Swedish, the former three because there is a large volume of literature available on the subject of palaeolinguistics and history, the latter two because I just like them.
I have my whole life ahead of me and I plan to live a very long one, and I'll spend most of it studying I guess. I can't tell how many of these languages I'll learn or even try to learn, but most of them require only passive understanding, and as I don't plan to really make anything of them except get to the knowledge I seek it is possible.
I'm currently learning Classical Greek and Old Church Slavonic.