Now here’s a topic that’s so basic, and useful, that I can’t believe I haven’t done it yet.
The informal Persian “thanks” should be very familiar to most of you: مرسی (marsī), or merci, en français. If you know Arabic, then the more formal-sounding “thank you” will also be familiar: مُتَشَکِّرَم (mutashakkiram), which takes the Arabic word متشکر, or “grateful/thankful,” and adds the short Persian ending for “I am,” so the whole thing is “I am grateful.” بِسیار مُتَشَکِّرَم (bisiyār mutashakkiram) means “thank you very much.” You may also say تَشَکُّر (tashakkur), another Arabic import that also means “thank you.” A more emphatic “thank you,” more “I’m really grateful,” or “I’m much obliged,” is خَیلی مَمنون (khaylī mamnūn), from yet another Arabic import (ممنون) that means “gratitude” or “obligation.”
“You’re welcome” is usually either خوش آمَدید (khūsh āmadīd, “khosh aamadeed”), which literally means “come well,” or خواهِش می کُنَم (khwāhish mī kunam, “khaa-hesh mee-konam”; that و is archaic in modern Persian and not pronounced, although it is pronounced in some other Iranian languages like Dari), which in a technical sense means “I beg” or “I request,” but has an idiomatic meaning here.