เลย is very commonly used as an intensifier in Thai, but an be difficult to translate directly into English. If it appears in combinations with abverbs such as มาก or จัง, which themselves serve to add emphasis to the sentence, then there's little need for a direct translation. If not, then a translation of "completely" or "totally" can work, or it might evade a direct translation and require a re-wording in English. In a negative sense, a ไม่....เลย combination can be translated as "not....at all" into English.)