Per note by Portugese translator on gnucash-devel, recommend change to step 5 in section 6.3.1 of the Help Manual. Currently, this paragraph reads:

5. When typing into the account field GnuCash will also attempt to automatically match the account name with an existing account. It does this alphabetically, so typing Ex will match the Expenses section of the account list. When the section is matched, it is possible to move to a child account by pressing : (colon). If after typing Ex you press : then the cursor will move to the first child account in the list. Typing combinations of letters and : will allow movement down the tree of accounts quickly. The triangle icon on the right of the Transfer box can be used as an alternate way of selecting accounts. Up & down arrow keys will also move up/down the displayed list of accounts. 

Recommended new text:

5. When typing into the account field GnuCash will attempt to automatically match the account name with an existing account. It does this alphabetically, so typing Ex will highlight the Expenses section of a typical account list. Once an account is highlighted, it is possible to move to a child account by pressing the account Separator Character (see below), which will then highlight the first child account in the list. Typing combinations of letters and the separator character will allow movement down the tree of accounts quickly. The triangle icon on the right of the Transfer box can be used as an alternate way of selecting accounts. Up & down arrow keys will also move up/down the displayed list of accounts.

Note: By  default, the account Separator Character is the colon (:). However, this character can be changed on the Accounts tab of GnuCash Preferences. See 10.2.2 or the Help manual for more information on changing the Separator Character.