However, it's important to consider the context and tone to find the most fitting translation in English. Here are some alternatives depending on the situation:
Formal:
* I'm at a loss for words.
* I'm speechless.
* I don't have the words.
Informal:
* I'm stumped.
* I'm speechless.
* I don't know what to say.
* I'm lost for words.
More nuanced:
* I can't find the right words.
* I'm struggling to find the words.
* I don't know what to say, but I'm so moved.
The best translation will depend on the specific situation and the overall tone of the conversation.