I work in ancient materials, so it's reading, not speaking that's needed. Reading wise, I'm pretty solid in Hebrew and Greek, ok in Syriac. In terms of modern academic languages I can read/write/speak German pretty well. I got a relatively late start on languages and actually consider myself somewhat behind. Before completing the PhD I'll need two languages more minimum, and preferrably four.

Before I refocused myself into Early Modern France, I was aiming to be a Classicist with a focus in the Late Roman Republic, so I had to learn Latin and Ancient Greek, the latter of which is still useful in my current focus on Early Modern France since the Habsburgs wrote laws in Latin first.

I am to learn French and Germany to further my ability in the subject as there are a lot of sources that haven't been translated or books that remain in their local language.

I'm studying for a BA in medieval studies, with emphasis on the British isles. Relevantly, I speak pretty good Latin, tolerable French, good Middle English, and beginning Old English. Less relevantly, I speak tolerable German and Spanish.

Latin American historian here. To graduate with a Ph.D. from my university, it was required that we have fluency in one foreign language relevant to our field, and reading knowledge of a second. I have fluency in Spanish, and reading knowledge of Portuguese. The Spanish is absolutely essential to me, and I use it constantly. I literally couldn't do my job without it. The "reading knowledge" of Portuguese I picked up in a six week class that basically taught what minor differences there were from Spanish. I wouldn't really say I'm fluent in any way. I can generally get the gist of what written things say. Honestly, I may find the Portuguese knowledge useful about once a year for something that I probably could have figured out about as well on Google Translate.

I will say that if I wanted to, I could go back to my same university (which I still live near) and pick up Mayan, Nahuatl, or Quechua, which are all offered as classes. Of those, Mayan would likely be the most useful to me, since I focus on Cuba and Mexico.

Studying African history, you would assume that speaking an African language would be useful. However, as I focus on colonies and the post-colonial period, nearly every written source is in English; government documents, memoirs, newspapers, etc. I was lucky enough to learn Afrikaans growing up which means I can make use of any journal articles published in Afrikaans (not that there are many) and I learnt chiShona to help me converse with people when conducting interviews, but honestly, I could do as well just knowing English. However, I have found that despite the majority of people I have interviewed speaking English fluently (you would be hard pushed to find anyone outside of the really rural parts of Zimbabwe who doesn't have a good grasp of English), they really appreciate you making the effort to converse in their own language. It makes them a lot more comfortable and, in my opinion, makes it a lot easier to actually have a conversation with them.

As a side note, I'm currently learning Portuguese (when I can!) to help with possible future work on Mozambique - now that is a field in which lots of work done is not in English, so Portuguese really is a necessity!

I'm a literary scholar of late 18th century texts focusing on England and France. I've definitely felt that I have to read French in order to be effective in my work, not only for the sake of reading original texts without translation, but also because there are many academic works in French pertinent to my field that have simply not been translated yet.

I'm less than a year into my PhD so its still a work in progress but I'm confident I'll be able to read French quite effectively by the end of the summer. I imagine the pressure to be familiar with the languages you study might be somewhat lesser for a non-literary historian, but I cannot imagine a scenario where it is not beneficial to your research or resume.

South Asia, it's the main thing (I need about half a dozen languages, I've got two down) between me and being a real scholar (as opposed to an apprentice).

I am a Japanese scholar, with native level fluency in ancient and modern Japanese. The ancient Japanese is restricted to reading of course, since we have no clue what the speaking actually sounded like. I have done some attempts at calligraphy in ancient style just for fun (it wasn't great).

I do a lot of work in the primary literature, both for the sake of understanding it as literature and as a source of insight for general history. It is obviously 100% indispensable to be able to read old Japanese in order to do any kind of work in the field. If you tried to do it by just reading in translation, your work would be invalid at worst or very limited at best.

Whilst since finishing my first year, my Koine Greek needs some brushing up, I have noticed, found, and been told that in order to be taken seriously in your field of study, an understanding of the main language(s) involved is essential. E.g. Latin and Greek for classics or theology (+ Hebrew), but also German as historically that's an important academic language through what they provided to academia, philosophy and theology especially.

For example, as a student of theology/New Testament Studies/etc, a good grasp of at least Greek is really what you should have. That is because it allows you to interact with the actual manuscripts, rather than just going off translations. Words such as harpagmos can have a number of different words when translated into English, and the meaning can change depending on who is doing the translating with what agenda they come from, or simply just by how you interpret 'exploited' (possible translation) compared to another English speaker.

One of my lecturers (holds a doctorate), learnt German when studying theology, and not just theology but philosophy, it has been helpful to him a lot (along with being taken seriously in the field of study). He's an Oxford graduate and studied in Germany too. Same with one of the Canon Theologians at the nearby Cathedral. He is very knowledgeable on Hegel and other philosophers, and so knowing the language is really important in academic studies. Not necessarily being fluent in speech, but at least in understanding written documents.

With that, dead languages such as Latin or Greek, you don't need speech-fluency for obvious reasons. Just being able to read it is the bare essentials, with writing being a bonus.

Back when I was doing Egyptology almost exclusively I had to know pretty good French and at least some German to sift through a lot of sources, and I also acquired the hieroglyphic portion of the Ancient Egyptian language.

Then I shifted to general Classics, which required me to learn Latin, Medieval Latin and Ancient Greek. I tried Italian for a bit, but dropped it because I was doing too much other stuff, but I think I'll go back to it soon.

If I want to continue studying the history of the Ancient world I'll need to pick up Italian for sure, as well as Biblical Hebrew, and maybe the other writing systems of the Egyptian language and the languages it turned into (Demotic and Coptic). I also think it'd be awesome to learn Old Norse so I bought some books for that, but haven't had the time to do it seriously yet.

tl;dr English, French, German, Ancient Greek, Latin, and Middle Egyptian, for now.