I hope this question gets answered even if it's (most likely)a silly one. Let's say I'm interested in Mayan history, there's plenty of information written about them in English, but must likely there would be much more data in Spanish, the language spoken currently in Mexico and Central America.
If I Wanted to make an extensive review on a particular subject (for example: Classical period Mayans and their relationship with Teotihuacan) should I use Spanish language sources as well or I could manage with only sources in English?
Is it common for historians to inmerse themselves in secondary sources written in other languages (and if they do, do they use a translator?) or historians usually stick to thier native languages.?
At least in my field, ancient history, historians are expected to be able to read several modern languages. French and German are absolutely mandatory (PhD students must pass translation exams in them), Italian is strongly recommended, and, depending on your specialty, Greek, Turkish, and/or Arabic are quite useful. It's very common for speakers of a particular language to dominate the scholarship of a region due to the lingering effects of colonialism; for example, most of the key publications on ancient Syria are in French, Germans dominate the scholarship of ancient Turkey, almost all relevant publications on ancient Cyprus are in English, and most works on the archaeology of Turkmenistan and other areas of Central Asia are in Russian. Well-balanced scholarship must engage with these sources, and dissertations or books that rely too heavily on English sources are (quite rightly) criticized for failing to address relevant scholarship done in other languages.
That said, you can hardly be expected to read every language under the sun, and occasionally a relevant paper eludes your bibliography due to being written in an unexpected language. My initial dissertation proposal was tossed out because my advisor knew a student in Japan had just written on the exact same topic. Since virtually nothing in my field is written in Japanese, I hadn't even thought to look for such a paper.
As u/Bentresh said, in basically every field, if you want to be taken seriously you must be able to read all of the relevant historiography in the major languages of your discipline. It's just not an option not to. You'll get away with only using English language sources at undergrad level and probably even at masters (although it's not advisable) but you'll be laughed out of the room if you try to write a PhD or submit a peer-reviewed article without showing that you've a good grasp of all the relevant languages (and more importantly, the primary sources and historiography in those languages).
Obviously the languages you need will vary wildly, mostly based on where and when you're studying, but it's imperative to know how to read them!