I'm fairly fluent in Hebrew, to the point where I speak it intuitively, often accidentally when I intend to speak English. But I struggle to think in it. My question is, what is required to think in a language? I know a lot of it has to do with culture, but is there a minimum vocabulary, or and other requirements?
Start with thinking about a topic that is related to the activities you do in your target language. If you read novels or watch films, think about the plot. If you chat with people, think about what they told you, or about what you want to tell them. If you attend lectures, take notes in the target language and learn from them without using your native language.
You may soon find out that thinking about L2 activities in L2 is actually easier than thinking about them in L1. That happens because when you do something in L2, you unconsciously learn new words, and they often don't have exact equivalents in L1. Therefore, it is natural that thinking about them in L2 is easier, even if your L2 level isn't very high.
Don't be worried, it takes years to begin thinking in a second language.
According to Fluentin3Months,
Thinking in a new language is a decision you can make. If you know even a few dozen key grammar words you can begin to think in your target language thanks largely to the 80/20 rule in language learning. It is easier than speaking in the language because you will not be embarrassed (unless you have a malicious alter-ego). It requires less confidence but more motivation than speaking.
During the early stages you may be using more of your native language than your target language, and that is fine. You will also probably be translating at first rather than “thinking fluently,” and that is fine, too. What is important is that you make a conscious effort to use the target language in your thoughts, not just in your conversations.
To keep up motivation, I highly suggest a journal (digital or analog) that you keep with you at all times. When you don’t know how to say (ahem, think) a key word just write it down. At the end of the day look up the words, or even better, ask a native. You now have a list of practical vocabulary to learn (instead of studying “shoelaces” and “aardvark” from a book)! For extra credit, date each entry – you’ll begin to notice how much smaller your daily lists get (and how much more esoteric). That’s progress you can see!
In addition, keep in mind that our minds are built to match patterns and sequences, so if I am studying French flashcards and you suddenly talk to me, often my first reaction will be to speak in French - at least until the context shifts. A few other things you can try are to surround yourself with native speakers, visit the country where the language you are learning is prominently spoken, and change your phone/computer to the target language (recommended for more intermediate learners).
From my experience, I suddenly found myself thinking in English (second language) when I had argued in English a lot in a company, then went out and still thinking about the matter of the argument, continued in my mind discussion, seeking persuasive words etc.
The language level: during the argue for me there was no need to think "how to translate (something)?" or "how to compose sentence?", "how to say it?" etc.