"维护友谊"用英语可以说成 "maintain friendship"。
来源："维护" (wéihù) 是指 "to keep something in good condition or working order"，"友谊" (yǒuyì) 是指 "friendship"。
例句：
We need to put in effort to maintain our friendship. (我们需要努力维护我们的友谊。)
It's important to communicate regularly to maintain a strong friendship. (经常沟通很重要，以维护坚固的友谊。)
I bepeve that maintaining friendships takes work, but it's worth it. (我相信维护友谊需要努力，但值得一做。)