update docs

Signed-off-by: Nshawn_he <shawn.he@huawei.com>

en/application-dev/internationalization/i18n-guidelines.md

-# Internationalization Development (i18n)
+# Internationalization Development (I18N)
 
-This development guide describes how to use i18n APIs that are not defined in ECMA 402.
+This module provides system-related or enhanced I18N capabilities, such as locale management, phone number formatting, and calendar, through supplementary I18N interfaces that are not defined in ECMA 402.
+The [Intl](intl-guidelines.md) module provides basic I18N capabilities through the standard I18N interfaces defined in ECMA 402. It works with the I18N module to provide a complete suite of I18N capabilities.
 
 ## Obtaining System Language and Region Information
 

en/application-dev/internationalization/intl-guidelines.md

-# Internationalization Development (intl)
+# Internationalization Development (Intl)
 
-This development guide describes how to use i18n APIs that are defined in ECMA 402.
+This module provides basic I18N capabilities, such as time and date formatting, number formatting, and string sorting, through the standard I18N interfaces defined in ECMA 402.
+The [I18N](i18n-guidelines.md) module provides enhanced I18N capabilities through supplementary interfaces that are not defined in ECMA 402. It works with the Intl module to provide a complete suite of I18N capabilities.
 
 > **NOTE**<br>
 > In the code snippets in this document, **intl** refers to the name of the imported module.

en/application-dev/reference/apis/js-apis-i18n.md

-# Internationalization – i18n
+# Internationalization – I18N
 
 > **NOTE**<br>
 > - The initial APIs of this module are supported since API version 7. Newly added APIs will be marked with a superscript to indicate their earliest API version.
 >
-> - This module contains enhanced i18n APIs, which are not defined in ECMA 402.
+> - This module provides system-related or enhanced I18N capabilities, such as locale management, phone number formatting, and calendar, through supplementary I18N interfaces that are not defined in ECMA 402. For details about the basic I18N capabilities, see [Intl](js-apis-intl.md).
 
 
 ## Modules to Import

en/application-dev/reference/apis/js-apis-intl.md

-# Internationalization – intl
+# Internationalization – Intl
 
 > ![icon-note.gif](public_sys-resources/icon-note.gif) **NOTE**
 > - The initial APIs of this module are supported since API version 6. Newly added APIs will be marked with a superscript to indicate their earliest API version.
 >
-> - This module contains standard i18n APIs, which are defined in ECMA 402.
-
+> - This module provides basic I18N capabilities, such as time and date formatting, number formatting, and string sorting, through the standard I18N interfaces defined in ECMA 402. For details about the enhanced I18N capabilities, see [I18N](js-apis-i18n.md).
 
 ## Modules to Import