According to some German Wiki the wording is:
"Stadt des Lichts (Bonus für große Werke verdoppelt in der Hauptstadt)"
'Great Arts' however seem to have been translated as 'Meisterwerke' elsewhere in the game. So there definitely is a good chance of people misunderstanding 'große Werke' for 'größere Bauprojekte' (large Construction Projects aka Wonders).
Also: the "Theming" got completely lost in translation. I don't see a reason why it shouldn't be "Thematikbonus" or "Themenbonus" instead of just 'Bonus'. It is a bit tricky; a real museum would probably talk about 'Schwerpunkte" but "Schwerpunktbonus" doesn't really work here.
And finally: wrong grammar/syntax. It should be:
"Stadt des Lichts (Themenbonus für Meisterwerke in der Hauptstadt verdoppelt)".
...and I have the feeling this isn't the only time where this happened
edit) from the same Wiki:
[Assyria UA]
-Wenn eine Stadt erobert wird, erhaltet ihr eine kostenlose Technologie, die der Besitzer schon erforscht hat. Der Erhalt einer Stadt durch ein Handelsabkommen wird dabei nicht berücksichtigt, und dies kann nur einmal
pro Spiel geschehen.
--> It says once per game instead of once per city.
[Brazil UA]
-Die Tourismusproduktion beträgt in Goldenen Zeitaltern 100%.
--> Wow really? My special is that instead of 100% I get... still 100%? Should be +100% or rather:
"Doppeltes Tourismusaufkommen während eines Goldenen Zeitalters."
-Große Künstler, Musiker und Schriftsteller tauchen in Goldenen Zeitaltern 50% schneller auf.
--> First of all: "Groß(e/r)" is horrible. It should rather be "Bedeutende(r)" or "Großartige(r)".
And then "auftauchen"... :facepalm:.
One should stick to the game mechanic here and say "Bedeutende Künstler, Musiker und Schriftsteller
werden während eines Goldenen Zeitalters 50% schneller
generiert."
[Portugal UA]
-Ressourcenvielfalt bringt Portugal doppelt soviel Gold [
in internationalen Handelsrouten] <-- this just got lost (still, I haven't set the game to German, but I doubt the guys in the wiki are that bad when it comes to copy and pasting). It is also very misleading (albeit the English wording also might cause the same misunderstanding) and I bet most people think the whole trade route would give double gold, not just the resource diversity part of it. So a better phrase would be: "Ressourcenvielfalt erhöht den Goldbonus in internationalen Handelsrouten um doppelt soviel wie normal". It's still misleading a bit, but better.
Ironically it would absolutely not be misleading in both English and German if the detail (the doubling) would be dropped and instead just be said, that resource diversity grants more gold than usual in intl. trade routes.
[Morocco UA]
-Erhält +3 Gold und +1 Kultur für jeden Handelsweg mit Zivilisationen oder Stadtstaaten.
The "different" got completely lost. I do like the Handelsweg here though (unless 'route' was translated to 'Weg' instead of 'Route' everywhere in the game^^ [edit: yeah... this seems to be the case]). Anyway:
"Erhält pro Zivilisation (oder Stadtstaat) zu der ein Handelsweg besteht +3 Gold und +1 Kultur."
[Indonesian UA]
-Gewürzinselbewohner (Spice Islanders) --> change to "Gewürzinsulaner".
[Venice UA]
-Händler von Venedig (Merchant of Venice) --> should be called 'Venezianischer Händler' [unless this causes "venezianischer Venezianischer Händler" to show up in the game

- in that case I think it's better to say 'Händler
aus Venedig' (instead of 'Händler
von Venedig')]
Hooray for "Weites Land" (Great Expanse [Shoshone])! - this is much better than the literal translation (Große Ausdehnung) would be.
Moderation might split my posting to a new/existing thread where this matter is already discussed. Hard to believe no one complained about that yet... guess people are used to mediocre translations by now (or even most Germans don't know what's proper German nowadays).