"Long time no see" is 好久不见 in Mandarin. I would be inclined towards adding a 了 at the end. Would that be all right? And in that case, what does the 了 add?
Technically speaking, 好久不见 and 好久不见了 are both acceptable;
了 completes the implicit meaning of "no see" as "have not seen" but can be omitted.
IMHO, the two are more or less interchangeable and it is merely a personal preference of which to use (I prefer the later as well). Nevertheless, from my experience, people usually use the former in relatively formal context. As to myself, I use
了 as a modal particle in this context, as in "Sigh/Wow/Damn, it's been long". I feel that it somehow extends or emphasizes the feeling at the moment.
On a side note, "long time no see" is commonly believed as originated from Chinese-speaking communities in the States, i.e. it is seen as Chinglish (Please forgive my language).
Means long time no see,
the "le" doesn' make any sense, 是语气词
the "le" doesn't make any sense, it's a modal word.
Modal words are auxiliary words showing tone, often used at the end of a sentence or in the middle at a pause to show all kinds of tone. Among common tone words there are: de, le, me, ne, ba, a. Modal word: attached to the end of a word or sentence, showing tone.
As othera have already pointed out, 了doesn't have explicit meaning. It's an exclamation 叹词 marking a statement. There are also exclamation words that mark excitement (啊 呀 呢 吧 啦) or question (吗 呢). Note some words can be used in a question or a statement depending o the tone you said it with… If you are not yet confused at this stage, here are two examples to play with: 我们很久没见了呢！ - long tiime no see! 我们多久没见了呀？- how long has it been?