You may add the calling of the mentioned addJsTranslation to the sys_injections table. Just place there the service call of your code:

INSERT INTO `sys_injections`(`name`, `page_index`, `key`, `type`, `data`, `replace`, `active`) VALUES
('sys_head', 0, 'injection_body_class', 'service', 'a:4:{s:6:"module";s:6:"system";s:6:"method";s:18:"add_js_translation";s:6:"params";a:1:{i:0;s:10:"body_class";}s:5:"class";s:21:"TemplTemplateServices";}', 0, 1);

Smth like that. Be sure that you use your own module, this system part has been give as example.