A method for periodic checking of localized lines in the application source code before the assembled application is propagated into message files (*.po). An automated internationalization of lines for all supported application languages is provided. The lines and their translations in locale files (JSON) are validated against the message files (PO). The un-localized lines are checked in the source code using a localization marker. According to the APS, a special trap (i.e., a hook) is used for APS msgmake utility in order to derive localization data from a set of aps_command_line_tools for assembling a user interface. The lines are corrected and loaded back into “*.po” file.