As mentioned before you may enter "true" or "false", also 1/0, yes/no, t/f, and y/n as possible values for booleans depending the content language. To find out about (and possibly change) the booleans used in your language, see the messages MediaWiki:Smw_true_words and MediaWiki:Smw_false_words.
See the effect for this wiki at: Help:Examples for boolean values pairs
Localization and multilingual content based on user language is provided with the #LOCL output formatting option. Furthermore, if a page has set a specific page content language 1 then the Help:DataValue tries to match local values against that language 2 instead of the global content language.
References
- ^ Semantic MediaWiki: GitHub issue #1580 example - Localization of boolean values
- ^ Semantic MediaWiki: GitHub pull request gh:smw:1580
