If you have proficiency with something, you are pretty good at it. If you have proficiency with Spanish, you can understand and communicate well in that language.
Proficiency, pronounced "pro-FISH-en-cee," comes from the Latin word proficere, meaning "accomplish, make progress, be useful." If you have achieved proficiency is something, you have done well at gaining a skill. However, having proficiency doesn't make you an expert. Still, proficiency is something to be proud of — it means you have worked hard, and if you keep going, you probably will become an expert.