Translation:Please give me a like.
Does this sound natural to Mainland Chinese ears with 一个 (after all, the amount is already implied, even if you leave it out)? In Taiwan I only ever heard 请给我按赞.
"a" means "一个". In the Taiwan context you mentioned, that could have a slightly different translation. "请给我按赞" = "Please hit/press me a like (button)", where 按 = press/hit.
A quick search gave numerous hits for "给我一个赞"，"给我点赞"， "给我按赞" and " 給我一個讚". So all of these are commonly used but like another user has noted they have slightly different meanings.
Hi, I'm Taiwanese. I seldom hear that. Usually is 請給我一個讚 or 幫我按（點）讚。
請給我按讚 is sounds an order, not a request. I think it's rude.