Learn Russian: Менеджер часто одалживает мне их степлер. - The manager often lends me their stapler.

In Russian, the third-person possessive pronouns (его, её, их) are indeclinable. This means they never change their form, no matter the gender, number, or case of the noun they belong to. Even though степлер is in the accusative case here, их stays exactly the same.

Wait, is степлер in the nominative case here?

It looks like it, but it is actually in the accusative case because it is the direct object (the thing being lent). Because степлер is a masculine, inanimate noun, its accusative form is identical to its dictionary (nominative) form.

Why is мне used instead of меня?

The verb одалживать (to lend) requires the dative case for the person receiving the object, just like in English when you give or lend something to someone. мне is the dative form of я. The direct object (the stapler) takes the accusative case.

I thought одалживать meant 'to borrow'. How do we know it means 'lends' here?

The verb одалживать is tricky because it can mean both 'to lend' and 'to borrow'! You have to rely on the grammar around it. Here, the dative pronoun мне tells us the action is directed to me (lending). If the manager were borrowing it from me, the sentence would use the phrase у меня instead of the dative мне.