You can say 一生の友達 (isshou no tomodachi) to mean "friends forever". Its literal meaning is "lifetime friends", and this makes sense when you think about religion in Japan over time, which has had little to do with a reunion-based afterlife and more to do with Buddhist/Hindu philosophies, thus two people being "friends forever" would be seen as impossible and the term "lifetime friends" is used.
"Eien ni yuujin" would be a way to say it.
"Itsumademo yuujin" is another way.
You can insert 'tomodachi', 'tomo' instead of yuujin (yuujin casualy means very close friend, best firend, chum).
You can say friends forever in Italian by saying amici per sempre. Friends forever in Russian is druz'ya navsegda. Friends forever in Spanish is amigos para siempre.
Eien ni kōjō sa seru is forever improving but this is not as good in Japanese as Tsuneni kaizen always improving
Watashitachiha tomodachi
'Itsu made matte mo ii.'
MUGEN means unlimited EIKYUU means forever
forever
You can say friends forever in Italian by saying amici per sempre. Friends forever in Russian is druz'ya navsegda. Friends forever in Spanish is amigos para siempre.
'Fuhen no ai.'
Eien ni watashino
Shin'yū eien ni
16
Eien ni kōjō sa seru is forever improving but this is not as good in Japanese as Tsuneni kaizen always improving
tyyni suula!
Watashitachiha tomodachi
Best Friends or Best Friends Forever or Best Friends For Life ;)
Amigos para sempre
'Itsu made matte mo ii.'