Transcription in Chinese characters
"ai shi bu ke ni de" is 愛是不可逆的.
Both are grammatically correctly and literally correct. In textbook grammar, it is a pattern of subject + "是" (verb to be) + an adjective (a phrase ended with 的).
龜是硬的。 Tortoise is hard.
鬼是恐佈的。 Ghost is terrific.
不可逆的 and 不可逆轉的 are phrases ended with 的. Actually they are negation of 可逆的 and 可逆轉的 correspondingly.
可 is commonly used in translation of -(a)ble in English.
In more advanced usage, 是 and 的 are optional. We could write 愛不可逆 and 愛不可逆轉 as well.
"不可逆的" is accurate translation of irreversible. But Chinese readers may not get its meaning. Or they may conceive that love is something that cannot be resisted or disobeyed.
While 愛是不可逆轉的 is grammatically and literally correct for translating "love is irreversible", it is not so comprehensible for Chinese readers.
逆轉 usually describes that a situation is reversed, from good to bad, or from bad to good. If one is in love, it is 愛. If one is no longer in love, it is 不愛. 愛 could change to 不愛. 逆轉 is problematic when it describes 愛.
You make a nice elaboration in your comment. "'Love' or the emotion is something that when given by somebody is difficult to take it back or to reverse that decision once taken."
In search for better translation, your comment reminds me a line "愛是可發不可收" in the lyrics from a Cantonese song 愛在深秋, sung by Alan Tam (譚詠麟), written by lyrist Andrew Lam (林敏聰). 可發 is "able to give" and 不可收 "unable to take it back". But it is poetic and somehow ambiguous.
There are some more idiomatic phrases like 覆水難收. 覆水難收 literally means "Spilt water can't be gathered up". We use it to describe "What is done can't be undone". But I would hesitate to write 愛是覆水難收. It looks like that "love is put to the end and is not recoverable"
Chinese would use "split water" to describe something that unable to get back. It would be more understandable to write 愛如潑水不可收, literally "love is like split water and one cannot take it back.
Alternatively, we can write 愛過無法磨滅. (Once) loved, (there is) no way to remove (the fact, its trace, its memory).
There are many words to describe "irreversible". But "love is irreversible" has implicit meaning and it is very difficult to translate it directly without misleading.