There was just some confusion over the directory mentioned, which didn't fit expectations. But you've explained that. No biggie.
Are you saying that the directory isn't there, or the file? Either way, have you tried putting the file in place where it's being looked for? I can't offer you anything as to why it should not be there, but perhaps putting it in place would help? This is my version:
[Desktop Entry]
Encoding=UTF-8
Type=XSession
Exec=/usr/bin/startkde
TryExec=/usr/bin/startkde
DesktopNames=KDE
Name=Plasma
Name[ar]=بلازما
Name[ast]=Plasma
Name[bs]=Plazma
Name[ca]=Plasma
Name[ca@valencia]=Plasma
Name[cs]=Plasma
Name[da]=Plasma
Name[de]=Plasma
Name[el]=Plasma
Name[en_GB]=Plasma
Name[es]=Plasma
Name[et]=Plasma
Name[eu]=Plasma
Name[fi]=Plasma
Name[fr]=Plasma
Name[gl]=Plasma
Name[he]=פלזמה
Name[hu]=Plasma
Name[id]=Plasma
Name[is]=Plasma
Name[it]=Plasma
Name[ja]=プラズマ
Name[ko]=Plasma
Name[lt]=Plasma
Name[nb]=Plasma
Name[nds]=Plasma
Name[nl]=Plasma
Name[nn]=Plasma
Name[pa]=ਪਲਾਜ਼ਮਾ
Name[pl]=Plazma
Name[pt]=Plasma
Name[pt_BR]=Plasma
Name[ru]=Plasma
Name[sk]=Plasma
Name[sl]=Plasma
Name[sr]=Плазма
Name[sr@ijekavian]=Плазма
Name[sr@ijekavianlatin]=Plasma
Name[sr@latin]=Plasma
Name[sv]=Plasma
Name[tr]=Plazma
Name[uk]=Плазма
Name[x-test]=xxPlasmaxx
Name[zh_CN]=Plasma
Name[zh_TW]=Plasma
Comment=Plasma by KDE
Comment[ar]=بلازما كدي
Comment[ast]=Plasma por KDE
Comment[bs]=Plazma od strane KDe
Comment[ca]=Plasma pel KDE
Comment[ca@valencia]=Plasma pel KDE
Comment[cs]=Plasma z KDE
Comment[da]=Plasma fra KDE
Comment[de]=Plasma von KDE
Comment[el]=Plasma από το KDE
Comment[en_GB]=Plasma by KDE
Comment[es]=Plasma, por KDE
Comment[et]=KDE Plasma
Comment[eu]=KDEren Plasma
Comment[fi]=Plasma KDE:ltä
Comment[fr]=Plasma, par KDE
Comment[gl]=Plasma por KDE
Comment[he]=פלזמה באמצעות KDE
Comment[hu]=Plasma a KDE-től
Comment[id]=Plasma oleh KDE
Comment[is]=Plasma frá KDE
Comment[it]=Plasma di KDE
Comment[ja]=Plasma by KDE
Comment[ko]=KDE Plasma
Comment[lt]=Plasmą sukūrė KDE
Comment[nb]=Plasma av KDE
Comment[nds]=Plasma vun KDE
Comment[nl]=Plasma door KDE
Comment[nn]=Plasma frå KDE
Comment[pa]=KDE ਵਲੋਂ ਪਲਾਜ਼ਮਾ
Comment[pl]=Plazma dzięki KDE
Comment[pt]=Plasma do KDE
Comment[pt_BR]=Plasma do KDE
Comment[ru]=KDE Plasma
Comment[sk]=Plasma od KDE
Comment[sl]=KDE Plasma
Comment[sr]=Плазма од КДЕ‑а
Comment[sr@ijekavian]=Плазма од КДЕ‑а
Comment[sr@ijekavianlatin]=Plasma od KDE‑a
Comment[sr@latin]=Plasma od KDE‑a
Comment[sv]=Plasma av KDE
Comment[tr]=KDE Plazması
Comment[uk]=Плазма KDE
Comment[x-test]=xxPlasma by KDExx
Comment[zh_CN]=KDE 的 Plasma
Comment[zh_TW]=Plasma by KDE
X-KDE-PluginInfo-Version=5.8.7