GetThreadPreferredUILanguages function (winnls.h)

Article
10/13/2021

Retrieves the thread preferred UI languages for the current thread. For more information, see User Interface Language Management.

Syntax

BOOL GetThreadPreferredUILanguages(
  [in]            DWORD   dwFlags,
  [out]           PULONG  pulNumLanguages,
  [out, optional] PZZWSTR pwszLanguagesBuffer,
  [in, out]       PULONG  pcchLanguagesBuffer
);

Parameters

[in] dwFlags

Flags identifying language format and filtering. The following flags specify the language format to use for the thread preferred UI languages. The flags are mutually exclusive, and the default is MUI_LANGUAGE_NAME.

Value	Meaning
MUI_LANGUAGE_ID	Retrieve the language strings in language identifier format.
MUI_LANGUAGE_NAME	Retrieve the language strings in language name format.

The following flags specify filtering for the function to use in retrieving the thread preferred UI languages. The default flag is MUI_MERGE_USER_FALLBACK.

Value	Meaning
MUI_MERGE_SYSTEM_FALLBACK	Use the system fallback to retrieve a list that corresponds exactly to the language list used by the resource loader. This flag can be used only in combination with MUI_MERGE_USER_FALLBACK. Using the flags in combination alters the usual effect of MUI_MERGE_USER_FALLBACK by including fallback and neutral languages in the list.
MUI_MERGE_USER_FALLBACK	Retrieve a composite list consisting of the thread preferred UI languages, followed by process preferred UI languages, followed by any user preferred UI languages that are distinct from these, followed by the system default UI language, if it is not already in the list. If the user preferred UI languages list is empty, the function retrieves the system preferred UI languages. This flag cannot be combined with MUI_THREAD_LANGUAGES.
MUI_THREAD_LANGUAGES	Retrieve only the thread preferred UI languages for the current thread, or an empty list if no preferred languages are set for the current thread. This flag cannot be combined with MUI_MERGE_USER_FALLBACK or MUI_MERGE_SYSTEM_FALLBACK.
MUI_UI_FALLBACK	Retrieve a complete thread preferred UI languages list along with associated fallback and neutral languages. Use of this flag is equivalent to combining MUI_MERGE_SYSTEM_FALLBACK and MUI_MERGE_USER_FALLBACK. (Applicable only for Windows 7 and later).

[out] pulNumLanguages

Pointer to the number of languages retrieved in pwszLanguagesBuffer.

[out, optional] pwszLanguagesBuffer

Optional. Pointer to a buffer in which this function retrieves an ordered, null-delimited thread preferred UI languages list, in the format specified by dwFlags. This list ends with two null characters.

Alternatively if this parameter is set to NULL and pcchLanguagesBuffer is set to 0, the function retrieves the required size of the language buffer in pcchLanguagesBuffer. The required size includes the two null characters.

[in, out] pcchLanguagesBuffer

Pointer to the size, in characters, for the language buffer indicated by pwszLanguagesBuffer. On successful return from the function, the parameter contains the size of the retrieved language buffer.

Alternatively if this parameter is set to 0 and pwszLanguagesBuffer is set to NULL, the function retrieves the required size of the language buffer in pcchLanguagesBuffer.

Return value

Returns TRUE if successful or FALSE otherwise. To get extended error information, the application can call GetLastError, which returns one of the following error codes:

ERROR_INSUFFICIENT_BUFFER. A supplied buffer size was not large enough, or it was incorrectly set to NULL.

If the function fails for any other reason, the parameters pulNumLanguages and pcchLanguagesBuffer are undefined.

Remarks

Depending on the flags specified by the application, this function can retrieve a composite list consisting of the thread preferred UI languages, process preferred UI languages, user preferred UI languages or system preferred UI languages, and the system default UI language. If it encounters a duplicate language, the function only retrieves the first language.

If the application has called SetThreadPreferredUILanguages with the MUI_CONSOLE_FILTER or MUI_COMPLEX_SCRIPT_FILTER flag, GetThreadPreferredUILanguages filters the languages in the result list. The function replaces the languages the console cannot display with a substitute language. The substitution for a language is determined from the value of LOCALE_SCONSOLEFALLBACKNAME for the language. For more console information, see the description of SetThreadUILanguage.

Use of MUI_LANGUAGE_NAME is recommended over MUI_LANGUAGE_ID because the MUI_LANGUAGE_NAME flag can do a better job of handling Language Interface Pack (LIP) languages that correspond to supplemental locales.

When MUI_LANGUAGE_ID is specified, the language strings retrieved will be hexadecimal language identifiers

that do not include the leading 0x, and will be 4 characters in length. For example, en-US will be returned

as "0409" and en as "0009".

If the application sets the MUI_LANGUAGE_ID flag, the thread preferred UI languages can include one or more languages that correspond to supplemental locales. On successful return from the function, the language buffer contains "1400" for any language corresponding to a supplemental locale. There can be only one such language in this list. The string "1400" corresponds to the hexadecimal value of LOCALE_CUSTOM_UI_DEFAULT. Also on successful return from the function, the pwszLanguagesBuffer contains "1000" for any other language that corresponds to a supplemental locale. The string "1000" corresponds to the hexadecimal value of LOCALE_CUSTOM_UNSPECIFIED, which is not useful as an input to any function, because it cannot distinguish among supplemental locales.

C# Signature

[DllImport("Kernel32.dll", CharSet = CharSet.Auto)]
        static extern System.Boolean GetThreadPreferredUILanguages(
            System.UInt32 dwFlags,
            ref System.UInt32 pulNumLanguages,
            System.IntPtr pwszLanguagesBuffer,
            ref System.UInt32 pcchLanguagesBuffer
            );

Requirements

Requirement	Value
Minimum supported client	Windows Vista [desktop apps only]
Minimum supported server	Windows Server 2008 [desktop apps only]
Target Platform	Windows
Header	winnls.h (include Windows.h)
Library	Kernel32.lib
DLL	Kernel32.dll

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