Please replace
{{#ifexist:Template:Main page/{{int:lang}}|{{int:lang}}|en}}
with
{{zh other|zh|{{#ifexist:Template:Main page/{{int:lang}}|{{int:lang}}|en}}}}
so that different Chinese variants (zh-hans, zh-hant, etc.) can correctly display the content of Template:Main page/zh (instead of Template:Main page/en).