i think it's more common to use underline for locales as like en_US, zh_CN.
and also in the java:
/**
* Returns a string representation of this <code>Locale</code>
* object, consisting of language, country, variant, script,
* and extensions as below:
* <p><blockquote>
* language + "_" + country + "_" + (variant + "_#" | "#") + script + "-" + extensions
* </blockquote>
*
* Language is always lower case, country is always upper case, script is always title
* case, and extensions are always lower case. Extensions and private use subtags
* will be in canonical order as explained in {@link #toLanguageTag}.
*
* <p>When the locale has neither script nor extensions, the result is the same as in
* Java 6 and prior.
*
* <p>If both the language and country fields are missing, this function will return
* the empty string, even if the variant, script, or extensions field is present (you
* can't have a locale with just a variant, the variant must accompany a well-formed
* language or country code).
*
* <p>If script or extensions are present and variant is missing, no underscore is
* added before the "#".
*
* <p>This behavior is designed to support debugging and to be compatible with
* previous uses of <code>toString</code> that expected language, country, and variant
* fields only. To represent a Locale as a String for interchange purposes, use
* {@link #toLanguageTag}.
*
* <p>Examples: <ul><tt>
* <li>en
* <li>de_DE
* <li>_GB
* <li>en_US_WIN
* <li>de__POSIX
* <li>zh_CN_#Hans
* <li>zh_TW_#Hant-x-java
* <li>th_TH_TH_#u-nu-thai</tt></ul>
*
* @return A string representation of the Locale, for debugging.
* @see #getDisplayName
* @see #toLanguageTag
*/
i think it's more common to use underline for locales as like en_US, zh_CN.![image](https://user-images.githubusercontent.com/7846605/125900097-bd5b2706-c4a3-4ede-84ab-0d08624391d0.png)
and also in the java: