Days before I experienced redirect loops when I tested the `tag search’ feature of SimpleTagging. I thought `Gengo should be worked something wrong.’ then I looked around Gengo’s setting pages and found that disabling `”Gengo should append language codes to permalinks automatically.’ feature could hide the problem.

Till today, I’ve killed off bugs in Gengo I’ve seen. I’ve got some knowledge of Gengo.

And finally I found `the solution’ to the issue.

open `Gengo Exclusions' page in admin panel, 
add "/tag" to `Exclusions' box.

Oh, yeah, the exact way is provided by the author.