[t0astbread]

Take what I say with a grain of salt because I'm not an industry veteran but I think a large part of fullstack is being able to transfer general skills across different areas and technologies (even outside of web development). So learning programming in general in any language that sounds good to you would probably be a good start.

As to what language to choose, I think every language has some quirks that will throw you off as a beginner. OOP languages (like Java or C#) used to be the classic first languages in courses but nowadays I think OOP is not as "critical" anymore. So something like Python or JavaScript would also work. A large online community helps, even if most of the advice online is terrible. (I read a lot of StackOverflow and random blogs/forums in addition to my classes at school when I learnt programming.)