Language preference feature has been implemented on version 2.1.1.0 or later.

You can download English language DLL from:
https://sourceforge.net/projects/sakura-editor/files/language2/

Unzip and put dll file in the same directory as "sakura.exe".
Start editor and choice language from [共通設定][ウィンドウ]-[言語].

Sources has been commited to:
https://svn.code.sf.net/p/sakura-editor/code/sakura/trunk2/sakura_lang_en_US

Improvement in the translation, or translation into other language is welcome.