Too bad you let the standard of English什么意思

糟糕，怎么让你说起标准英语啦！

let 这里是允许、让，许可的意思。

i am not sure either, maybe we can not interprete it just by this sentense,if you can give us about it in an article ,maybe it will be easier,I think/

太糟糕了你让的英语水平

爸爸让你学好英语的基础