@Boost I have the exact same need to see TinyMCE generating the uk-text-left class, instead the align_left one.
I tried dozents of JSON-instructions in Default setting overrides JSON text, i.e.
{
"replace_alignleft": {
"classes": "uk-align-left",
"selector": "img"
},
"replace_aligncenter": {
"classes": "uk-align-center",
"selector": "img"
},
"replace_alignright": {
"classes": "uk-align-right",
"selector": "img"
}
}
and changed the whitelist (.., img[class=uk-align-left|uk-align-right|uk-align-center], ..) to accept the new classes, but no effect.
Did you get it done and if, can you please share your JSON???