Specifying colors and fonts individually is deprecated (D2151), specify the object directly here, then we dont have to create it multiple times and it can be extended or changed by mods.

g_ObserverCountTags

good

Also if you/elexis want to minize, you could write something like this:

game.observerNumbers = stringifiedTeamListToPlayerData(game.players)).filter(() => { return player.Team == "observer" }).length;

I think counting of observers shouldn't be here? Because this is a sorting or filter.
So split on few lines at least.

The filter closure can be further simplified given it's only a single expression:

.filter(player => { return player.Team == "observer"});

.filter(player => player.Team === "observer");

Translators won't know what this is about, so it should have a translation comment:
// Translation: Number of observers in the gamelist
or similar

Don't split the translate and sprintf, so that people see the string arguments right near the string.
If we want to split that from the code logic to allow modders to change it more easily, then splitting both sprintf and translate would keep the string and its arguments grouped.

(> 0 unneeded I guesS)

Might be interesting to use setStringTags for this. See D2151.

+%(observercount)s or +%(observers)s?

non-bot players -> lobby players? Also seen "human player" somewhere. Otherwise bot -> AI.

(Its also not obvious whether thats a bug, whether it should reflect human players or ingame players including AI. For example 2 human vs 6 AI player looks like 2/8, as in 6 missing, but theyre not missing. Can be changed, but not sure if it should, also OT)

At least it would be consistent to make "gray" a global. And the more recent version of that would be to use setStringTags, so that people can also specify a font alongside if they want.

That += " " + is preventing translators to change the order of the arguments.

Same for playerText and the "/" operator.
Some languages might want to use a different symbol than slash, and thus also a different order.

So

// Translation: meaningful information
sprintf(translate("%(foo)s / %(bar)s")`...

(
On that > 0 check, I wonder if one could do some magic using plural strings.

translatePlural(singularMessage, pluralMessage, number)

But that won't work, since the english strings can only be specified for singular n=1 and plural n>1, but we need 0 and > 0 checks here.
(The translators can propose translations for arbitrary N intervals afaik)
)

One could say that the unification of the two sprintf's makes the close slightly slower, but then again one could care less if there are only < 30 games at a time and it costs probably something of the order of magnitude of 1 microseconds.