Learn Farsi: سفیر موسوی معاهده‌ی بین‌المللی را امضا می‌کرد. - Ambassador Mousavi was signing the international treaty.

In English, we just place the title next to the name. In Farsi, you must connect a title to a person's name using an Ezafe (an "-e" or "-ye" sound). Even though it is not written, it is pronounced safir-e musavi. This is the Explanatory Ezafe, which links titles or categories to proper nouns.

Why is there a ی (ye) attached to the end of معاهده (treaty)?

The word معاهده ends in a "silent he" (ه), which makes an "e" sound. When linking this noun to the adjective بین‌المللی (international) with an Ezafe, you cannot just add another vowel. Farsi uses the consonant ی to bridge them, creating the sound mo'ahede-ye.

Why is the direct object marker را placed after the adjective instead of the noun?

The particle را marks the entire definite direct object, not just a single word. Since the object receiving the action is the full noun phrase "the international treaty" (معاهده‌ی بین‌المللی), the را must be placed at the very end of that entire block.

How do we know the verb means "was signing" instead of just "signed"?

The compound verb امضا می‌کرد uses the prefix می attached to a simple past tense verb (کرد). In Farsi, adding می to the simple past creates the past continuous (or imperfect) tense, showing an ongoing or habitual action in the past.