Can we read English or Urdu translation of any dua in wajib namaz or in mustahab namaz?
1st Reason we don’t know how to read Arabic
2 Reason We want to understand what is written?

If you mean in qunoot, yes you can.
No doubt understanding is very important we must read translations of all surah and recitations before the prayer but we must read in Arabic.
Because entire namaz is in Arabic
Only in qunoot we are allowed to pray in our language but at the same request you to read small dua in Arabic also from Quran or taught by Ahlul bait as
Like Rabbana Aatena Fid Duniya Hasanatan wa fil Aakherate Hasanatan wa qena Azaban Naar