His Spanish isn't good,even after three years in Spain.

这里的 even 是副词，意思是“即使，甚至，连”，通常放在所强调的词语或者句子前面。在本句中，even 强调介词短语 after three years in Spain。又如：He wears socks even in summer. 上他即使在夏天也穿袜子。/ Even when I apologized to her, she still wouldn't talk to me. 即使在我向她道歉后，她都不肯跟我说话。（摘自2008年7月第1版《外研社英汉多功能词典》p.707）

His Spanish isn't good,even though he lived in spain for 3 years.

这里的 even though 表示“即使；虽然”的意思，是引导让步状语从句的连词。例如：

I would not do such a thing, even though I were to get a million dollars. 即使我能得100万元，我也不会做这种事。（摘自《刘毅英语语法宝典》p.526）

Nobody would help her,not even her best friend would help her.

没有人愿意帮助她，就连（即使）她最好的朋友也不愿意帮助她。

（这里的 even 是副词，）

Nobody would help her,and even her best friend would not help her.

这个句子与上一句意思相同，但是 not even ... 比 even ... not 的否定意味更强。

又如：Not even a dog can eat it. 甚至连狗都不能吃。(与 Even a dog cannot eat it相比，not 置于句首否定的意味更强)（摘自2008年7月第1版《外研社英汉多功能词典》p.707）