Text in buttons not displayed correctly (e.g. simplesearch or next / previous post)

[sklus]

Hi there,
I recently installed a Grav site, using the blog skeleton. The site is up and running, but for some reason, the content of buttons or placeholder text is not displayed correctly. Several examples:
Simplesearch plugin - search box: the placeholder instead of a “normal” text, shows “PLUGIN_SIMPLESEARCH.SEARCH_PLACEHOLDER”
Blog posts (items): At the end of each post, instead of “Previous post” or “Next post”, it says “THEME_QUARK.BLOG.ITEM.NEXT_POST” or “THEME_QUARK.BLOG.ITEM.PREV_POST”.

I already looked at the different twigs and it seems that under normal circumstances, they fetch some kind of constants, that (depending on the language) hold the actual value. I my case, only the constants’ name is displayed.

I already looked at the server’s log file and error files, but they seem ok; no errors shown.

Maybe someone has an idea; any help is appreciated.

Regards,
Sebastian

P.S.: I am attaching a screenshot to illustrate:

[sklus]

Answering myself… and feeling kind of stupid:
I set up a new site, completely from scratch, and there everything worked just fine.
So I started comparing (first plugins and then configuration) between the two sites, until I got to the configuration of languages and translations. As I was not thinking about a multi-lingual site, I disabled translations.
And enabling it again…
Thanks anyway