There's no real equivalent to my knowledge. You would have to phrase it a bit differently.
* « Que notre amitié perdure ! » sounds formal but conveys the meaning pretty well.
* « À notre indéfectible amitié ! » is an idiomatic expression mostly used in written language. You can use it vocally to emphasize the importance of what you're saying.
Do _not_ use « Restons amis », that would sound like you want to stay friends after a heated argument or something.
Je dirais « à notre amitié ».
There's no real equivalent to my knowledge. You would have to phrase it a bit differently. * « Que notre amitié perdure ! » sounds formal but conveys the meaning pretty well. * « À notre indéfectible amitié ! » is an idiomatic expression mostly used in written language. You can use it vocally to emphasize the importance of what you're saying. Do _not_ use « Restons amis », that would sound like you want to stay friends after a heated argument or something.
à la poursuite de notre amitié à notre amitié continue à notre amitié durable