[Doc] Update System_limit.md (backport #50542)

docs/en/reference/System_limit.md

@@ -19,7 +19,8 @@ This topic describes the rules and limits that apply when you use StarRocks.
   - Column name (column alias), partition name, and index name are **not** case-sensitive. Other names are **case-sensitive**.
 
 - Naming conventions for labels:
-  You can specify the label of a job when you import data. The label name can consist of underscores (\_), letters (a-z or A-Z), and digits (0-9), and cannot exceed 128 characters in length. The label name has no requirement for the starting character.
+
+  You can specify the label of a job when you load data. The label name can consist of digits (0-9), letters (a-z or A-Z), and underscores (\_), and cannot exceed 128 characters in length. Label names can start with a letter or an underscore (\_).
 
 - When you create a table, the key column cannot be of the FLOAT or DOUBLE type. You can use the DECIMAL type to represent decimals.
 

docs/zh/reference/System_limit.md

@@ -19,7 +19,7 @@ displayed_sidebar: docs
 
 - 对标签（Label）名的要求：
 
-  导入数据时可指定任务的标签（Label）。标签名可由数字 (0-9)、字母（a-z或A-Z），以及下划线(\_)组成，且长度不能超过 128 个字符。标签名对起始字符无要求。
+  导入数据时可指定任务的标签（Label）。标签名可由数字 (0-9)、字母（a-z或A-Z），以及下划线(\_)组成，且长度不能超过 128 个字符。标签名以字母或下划线开头。
 
 - 建表时，Key 列不能使用 FLOAT 或者 DOUBLE 类型，可用 DECIMAL 类型表示小数。