You've already done the first step, which is actually using FOSS software. That's the only way to get real context on what you're contributing to and find issues or lack of features that bothers you or is incredibly specific to your system or use case, and fix something that maybe would not have come up otherwise or no one would have time to get to.

Filtering issues by 'Good First Issue' as someone said is also a really good way to find tasks that are relatively easy to get your feet wet with a codebase. Don't feel bad about taking on too many of them, it's better that someone does them all and gains enough experience to become a regular contributor, than the rest of them collecting dust until someone else like you shows up.

Don't worry too much about not knowing X or Y language, the great thing about being into FOSS is that you get to become a multilingual developer, which is very eye opening and educational as opposed to sticking to a language like Java and never realizing the limitations it has or even the benefits it has relative to other languages, and use that knowledge to be a better engineer overall. It's easier to learn new languages nowadays, plenty of guides and docs to find, and AI can help for more specialized and context aware questions, just don't fall into the trap of letting AI do the job for you, you would only be fooling yourself.

Also don't underestimate the value of small contributions like documentation updates, translations, creating issues, etc. You don't need to come up with a PR for every issue you create, just finding things and keeping active is enough when you don't have the time or energy to go the whole way.