Log into the system and choose Accounts from theCONTACTS tab menu.
On the ACCOUNTS OVERVIEW you can see all the ACCOUNTS from a given language/region.
If an account does not have any contacts, then it has an empty 'L/R' property and is visible in all possible languages/regions. But if you add i.e. contacts from en_US and nl_NL to an account, then the account 'L/R' property will be en_US/nl_NL and this account will only be visible in en_US/nl_NL.
On the ACCOUNTS OVERVIEW you can also see 'SELECT FILTER' with a dropdown. Using this filter you can see ALL accounts or accounts starting with the letter you select.