Hello @Busimatch !

The usual pages in UNA should call the constructions like

$this->_oTemplate->addJsTranslation(array('_sys_grid_search'));

for calling of the translations in the dynamic JavaScript code. So it's impossible to use it for the custom pages and blocks. But you may use the following solution.

Create 2 blocks: 1 with the lang type (for the text) and 1 as the RAW (for the script). For the lang block you need to choose the "Content" variant for the Block Layout* parameter. And in the RAW block you may use the JQuery selectors like in the next example

<script>
	alert(_t($(".bx-page-lang-container").text()));
</script>

to take the proper key value. The .bx-page-lang-container CSS class may be hidden on the page or you may remove it with JS code too.