Note you might be interested in looking at interactive machine translation systems and the associated research papers - for example Lilt [1, 2] or TransSmart [3, 4] - while those are designed for professional translators rather than for language learners, what they do is very similar to your long-term aims for this project (a specialized MT system that, given a partially written translation to the foreign language and some context written in in the user's native language, suggests the following word).

[1] https://lilt.com/technology/translate [2] https://lilt.com/research [3] https://transmart.qq.com/ [4] https://arxiv.org/pdf/2105.13072.pdf