Das erklärt dann auch warum das Sprachpaket nicht installiert wurde. Was nicht da ist, kann nicht installiert werden
Welche Paketquelle hast Du eingestellt? Im nightbuild gibt es die Sprachpakete für epgsearch.
root@MLD-Test:~# apt search epgsearch
Sorting... Done
Full Text Search... Done
vdr-font-symbols/unknown 20100612-r0.0 amd64
This is a TrueType font that includes the symbols used by some VDR plugins and patches, e.g. ExtRecMenu v1.2test1, NordlichtsEPG v0.9test1, EPGsearch v0.9.24beta26, Music plugin and zulu's VDR Extensions Patch v56.
vdr-font-symbols-dbg/unknown 20100612-r0.0 amd64
This is a TrueType font that includes the symbols used by some VDR plugins and patches, e.g. ExtRecMenu v1.2test1, NordlichtsEPG v0.9test1, EPGsearch v0.9.24beta26, Music plugin and zulu's VDR Extensions Patch v56. - Debugging files
vdr-font-symbols-dev/unknown 20100612-r0.0 amd64
This is a TrueType font that includes the symbols used by some VDR plugins and patches, e.g. ExtRecMenu v1.2test1, NordlichtsEPG v0.9test1, EPGsearch v0.9.24beta26, Music plugin and zulu's VDR Extensions Patch v56. - Development files
vdr-plugin-epgsearch/unknown git-r0.27 amd64
VDR epgsearch plugin
vdr-plugin-epgsearch-dbg/unknown git-r0.27 amd64
VDR epgsearch plugin - Debugging files
vdr-plugin-epgsearch-dev/unknown git-r0.27 amd64
VDR epgsearch plugin - Development files
vdr-plugin-epgsearch-doc/unknown git-r0.27 amd64
VDR epgsearch plugin - Documentation files
vdr-plugin-epgsearch-locale-ca-es/unknown git-r0.27 amd64
VDR epgsearch plugin - ca_ES translations
vdr-plugin-epgsearch-locale-cs-cz/unknown git-r0.27 amd64
VDR epgsearch plugin - cs_CZ translations
vdr-plugin-epgsearch-locale-da-dk/unknown git-r0.27 amd64
VDR epgsearch plugin - da_DK translations
vdr-plugin-epgsearch-locale-de-de/unknown git-r0.27 amd64
VDR epgsearch plugin - de_DE translations
vdr-plugin-epgsearch-locale-el-gr/unknown git-r0.27 amd64
VDR epgsearch plugin - el_GR translations
...
Das wichtige fonts paket ist das vdr-font-symbols. Die Pakete mit -dbg und -dev sind nur für's Debuggen interessant, also nicht für normale User.