There are some issues with the supported "Up Next" addon.
When setting the display mode to "simple", the caption which should say something like "Next episode in ... seconds" shows "Hide Collection (Set) Marks ... seconds".
This is because in "script-upnext-upnext-simple.xml" the context is wrong.
script-upnext-upnext-simple.xml:
<label> $LOCALIZE[32239] [COLOR $VAR[LabelTextColor]]$INFO[Player.TimeRemaining(ss),,][/COLOR] $LOCALIZE[32047]</label>
"#32239" points indeed to "Hide Collection (Set) Marks".
Confusingly "#32238" is referenced two times and is also used in "script-upnext-stillwatching-simple.xml" to correctly show "Continue Watching in ... seconds". So maybe it helps to use an unused number for msgid "Next Episode in".
strings.po:
msgctxt "#32238"
msgid "Continue Watching in"
msgstr ""
msgctxt "#32238"
msgid "Next Episode in"
msgstr ""
msgctxt "#32239"
msgid "Hide Collection (Set) Marks"
msgstr ""
It seems that this issue is across all languages.