Team captains sometimes are, too.

(Though far below the WC level) many players are also on teams in countries other than their home nation. It is not unusual for players to be able to communicate in 3-4 languages. I knew swear words in 11 different languages.

English/French/Spanish are very common on the field. The conversations may be using multiple languages at the same time with a 3rd player helping interpret but the meaning gets across.

80% of the conversations are along the lines:

Ref are you blind
I saw it.
But we are innocent; they are cheating.
I’ll make the calls, you play the game.

I've always been jealous of folks who were raised around multiple languages. And I think the US would be in much better shape if we (US citizens) were also multi-lingual.

Signals tell everyone what they need to know. Otherwise, common languages and sometimes English, though there is no guarantee that the players or refs speak English.

How do the players on AC Milan communicate with each other, much less the referee, when they come from France, the US, England, Ghana, Germany, and Italy? At least in World Cup, all the players on the same team speak the same language (more or less).

The answer was given above: most will speak sufficient "football English" to communicate in English.

(To be fair, most players in any European league are from that country - AC Milan players and refs mostly speak Italian to each other; the foreigners - like US player Christian Pulisic - learn enough calcio Italian to communicate with the ref, or, more likely, the ref speaks English well enough).

Last night Austria played Jordan, the ref was Mauritanian - Arabic is the official language there.

Jordanians got to whine in their native tongue.

The Austrians probably used English.