Highest number of league teams represented in a national 11

[Sam]

And the Great Britain (/England, because they were invited by the FA rather than by all four associations) team that won gold at the 1900 Olympics was Upton Park FC in different shirts.

[Satchmo Distel]

USSR fielded a Dinamo Kiev eleven twice in 1975.

[Patrick Thistle]

Back in the day when the FA treated the other Home Nations with contempt, Wales fielded three non-league players against Scotland in 1930.
The FA refused permission for non-English players to be released from their Football League clubs for international duty meaning Wales had to select a team from Welsh clubs. Of the XI who played, Fred Keenor had 29 caps, Len Evans the keeper was winning his second cap whilst the other nine were debutants.

Len Evans (Cardiff City)
Fred Dewey (Cardiff Corinthians)
Wynne Crompton (Wrexham)
Billy Rogers (Wrexham)
Fred Keenor (Cardiff City)
Emrys Ellis (Nunhead)
William Collins (Llanelli)
John Neal (Colwyn Bay)
Thomas Bamford (Wrexham)
Walter Robbins (Cardiff City)
Billy Thomas (Newport County)

My Grandad said Tommy Bamford was the greatest player he ever saw play for Wrexham. He watched Wrexham from the 1920s (when he was a boy) into the late 90s at least, possibly even into the noughties. He died in 2009.

[Jorge Porbillas]

still our record goalscorer

[1974ddr]

Back in the day when the FA treated the other Home Nations with contempt, Wales fielded three non-league players against Scotland in 1930.
The FA refused permission for non-English players to be released from their Football League clubs for international duty meaning Wales had to select a team from Welsh clubs. Of the XI who played, Fred Keenor had 29 caps, Len Evans the keeper was winning his second cap whilst the other nine were debutants.

Len Evans (Cardiff City)
Fred Dewey (Cardiff Corinthians)
Wynne Crompton (Wrexham)
Billy Rogers (Wrexham)
Fred Keenor (Cardiff City)
Emrys Ellis (Nunhead)
William Collins (Llanelli)
John Neal (Colwyn Bay)
Thomas Bamford (Wrexham)
Walter Robbins (Cardiff City)
Billy Thomas (Newport County)

Isn't that four non-league players?

[Jorge Porbillas]

Good spot!

[Furtho]

Japan in the 2014 World Cup against Ivory Coast, a game the memory of which still causes me grave disappointment:

Kawashima (Standard), Uchida (Schalke), Nagatomo (Inter), Morishige (FC Tokyo), Yoshida (Southampton), Hasebe (Nuremberg), Yamaguchi (Cerezo), Honda (Milan), Okazaki (Mainz), Kagawa (Man Utd), Osako (1860 Munich)