'Geimu WA anata no make desu.'
The above is not correct gramatically, and considering what you're trying to translate, there's no need to be so formal, either.
"Omae ga geimu wo maketa" would work just fine.
Ushinawa
ikke
see Google Translate
'I lost' would be translated as私が負けた (watashi ga maketa) in Japanese.
私は試合に負けた, or Watashi WA shiai ni make ta.
Ko-Nenko desu ne?
terribee gamuu
ゲームオーバー Gēmuōbā
You just say "I'm sorry you lost!" If he played a good game, compliment him on how hard he tried, but don't say "good game" if he was goofing off and deserved to lose.
You may say 'geemu.'
The word 'games' would be translated as ゲーム(geemu) in Japanese. The words for 'games' and 'game' are the same in Japanese, as plurals are rarely used.
the US was pissed because they lost in a card game against japan