ICU-22520 doc: uloc_getName() & others may fail

for example with a U_ILLEGAL_ARGUMENT_ERROR since PR #2813
in some cases where the implementation may have
returned with a misleading U_BUFFER_OVERFLOW_ERROR

icu4c/source/common/unicode/uloc.h

@@ -399,6 +399,9 @@ uloc_setDefault(const char* localeID,
 /**
  * Gets the language code for the specified locale.
  *
+ * This function may return with a failure error code for certain kinds of inputs
+ * but does not fully check for well-formed locale IDs / language tags.
+ *
  * @param localeID the locale to get the ISO language code with
  * @param language the language code for localeID
  * @param languageCapacity the size of the language buffer to store the  
@@ -417,6 +420,9 @@ uloc_getLanguage(const char*    localeID,
 /**
  * Gets the script code for the specified locale.
  *
+ * This function may return with a failure error code for certain kinds of inputs
+ * but does not fully check for well-formed locale IDs / language tags.
+ *
  * @param localeID the locale to get the ISO language code with
  * @param script the language code for localeID
  * @param scriptCapacity the size of the language buffer to store the  
@@ -435,6 +441,9 @@ uloc_getScript(const char*    localeID,
 /**
  * Gets the  country code for the specified locale.
  *
+ * This function may return with a failure error code for certain kinds of inputs
+ * but does not fully check for well-formed locale IDs / language tags.
+ *
  * @param localeID the locale to get the country code with
  * @param country the country code for localeID
  * @param countryCapacity the size of the country buffer to store the  
@@ -453,6 +462,9 @@ uloc_getCountry(const char*    localeID,
 /**
  * Gets the variant code for the specified locale.
  *
+ * This function may return with a failure error code for certain kinds of inputs
+ * but does not fully check for well-formed locale IDs / language tags.
+ *
  * @param localeID the locale to get the variant code with
  * @param variant the variant code for localeID
  * @param variantCapacity the size of the variant buffer to store the 
@@ -471,6 +483,10 @@ uloc_getVariant(const char*    localeID,
 
 /**
  * Gets the full name for the specified locale.
+ *
+ * This function may return with a failure error code for certain kinds of inputs
+ * but does not fully check for well-formed locale IDs / language tags.
+ *
  * Note: This has the effect of 'canonicalizing' the ICU locale ID to
  * a certain extent. Upper and lower case are set as needed.
  * It does NOT map aliased names in any way.