Is it permissible to benefit from and work with the French language that was learned on the condition of shaving the beard?

There is no harm in working with this language, for the sin lies in shaving the beard, not in learning or working with the language. Seek Allah’s forgiveness for this sin, and do not exaggerate or delve too deeply into it, lest you fall prey to obsessive whispers and doubt. The Prophet, peace and blessings be upon him, said: "Perished are those who delve too deeply," meaning those who go beyond the limits.