You can change the software language in 'DesignSpark options'. You can find it by clicking on the DSM icon at the top-left corner of the software window or 'File' button.
DSM is currently available in 25 languages (as of version 5.0):
English, Bulgarian, Czech, Danish, Finnish, French, German, Hungarian, Italian, Japanese, Korean, Malay (Bahasa Melayu), Nederlands (Dutch), Polish, Portuguese (Brazil), Romanian, Russian, Slovak, Slovenian, Spanish, Swedish, Thai, Turkish, Chinese (Simplified), Chinese (Traditional)
Then, click on the 'advanced' tab.