Author: Jerome Mouneyrac
MDL-35997 Create web service functions to return lang strings
http://git.moodle.org/gw?p=moodle.git;a=commit;h=11e766020bd8e05b59550d3164e1a2cd20cc8ad9
http://github.com/moodle/moodle/commit/11e766020bd8e05b59550d3164e1a2cd20cc8ad9
+ 2.4 en [unamedstringparam,core_webservice]