Yes, you can add new words to the master phonetic lookup dictionary. This is a very good practice in a case like yours where there are words which are proper names with a very specific pronunciation but they derive from other languages (I almost recommended that you do that yesterday but I didn’t want to overwhelm you with info while you were still doing some initial troubleshooting, so I’m happy to see you figured it out). I wrote a blog post some time back about how to do it – the only big change you need to keep in mind now is that you can just directly edit LanguageModelGeneratorList.txt rather than using the methods described in the post:
So when you read the post, the import part is about the required formatting, order, and how to find the phonetic transcription for your new words for when you add things to AcousticModelEnglish.bundle/LanguageModelGeneratorList.txt, but you don’t have to worry about the programmatic stuff about how to reference a special custom file. If it’s working you’ll see the word found without having to fall back to the grapheme generator.