French phrase
Je vous en serais reconnaissant.
Meaning
I would appreciate it if you could.
When to use it
A polite expression of gratitude for a favor. It is especially suited to formal written requests.
Example dialogue
Pourriez-vous écrire une lettre de recommandation pour moi ?
Could you write a letter of recommendation for me?
Je vous en serais reconnaissant.
I would appreciate it if you could.