Fix the language and country format

BUG = XWALK-2361

Testing that language_info is en_US.utf8, but (LANGUAGE)_(REGION) syntax is required on the spec(https://developer.tizen.org/dev-guide/2.2.0/org.tizen.web.device.apireference/tizen/systeminfo.html#::SystemInfo::SystemInfoLocale), so fix it.