Every language has a two-digit language code that is used to tell your store what language is should be showing. Some languages have multiple versions/dialects, like Portuguese (Brazil) and Portuguese (Portugal). Typically, these languages would normally have a four-digit code instead, so Portuguese (Brazil would be "pt-br", and Portuguese (Portugal) would be "pt-pt". Shopify markets currently has a limitation, where only the two-digit version is supported. This means that these languages have the exact same code, which you can see below for both version of Portuguese and Chinese:
Since your store cannot have two different pages with the same code, you are only able to have one of these language versions active on the Market.
Shopify is aware of this limitation, but we do not yet know when it will be fixed.