Foreign languages are her strong suit?

That sentence is grammatically correct, but it's a bit awkward and could be improved. Here are some alternatives, depending on the context:

More natural and concise:

* She's very good at foreign languages.

* She excels at foreign languages.

* She's fluent in many languages.

* Foreign languages are her strong point.

More descriptive:

* She has a natural talent for learning foreign languages.

* She picks up languages easily.

* She's a gifted linguist.

The best choice depends on what you want to emphasize. If you want to focus on her ability to learn languages quickly, "She picks up languages easily" would be a good option. If you want to emphasize her fluency, "She's fluent in many languages" might be better.