Just to expand on this, at least in Mandarin, one types out phonetic Latin alphabet-based pinyin and the system prompts you with choices of matching symbols in the same way that predictive keyboards show you words. You select which characters to insert by clicking/tapping on them or hitting a number key. The only big difference is that the same pinyin might correspond to any number of characters and you might have to search through a lot, but context and frequency helps it suggest the right ones to you. (Mandarin only has 409 different pinyin 'syllables' when ignoring tones, which aren't typed in this system. Even with tones, there's only like 1200. These map to many thousands of characters, obviously not one-to-one. Depending on how you count, English has something like 16000 syllables.)