If you only speak Japanese in Japan, you can get by just fine.
You won't have any trouble living in Japan if you don't speak any other languages other than Japanese.
ーIf you only speak Japanese in Japan, you can get by just fine.
「日本で日本語しか話さなくても普通にやっていけるよ」
to get by で「何とかやっていく」
just fine で「普通に・まったく問題なく」
ーYou won't have any trouble living in Japan if you don't speak any other languages other than Japanese.
「日本語以外の言葉を話さなくても、日本で生活するのに全然問題ない」
don't speak any other languages other than Japanese で「日本語以外の他の言語をまったく話さない」
ご参考まで！
カナダ 
