translate library/string.rst:478 & 481 (#675)

* translate library/string.rst:478 & 481

* add space between chinese character and english character

* Update library/string.po

---------

Co-authored-by: Wei-Hsiang (Matt) Wang <mattwang44@gmail.com>

Author: vinachang

library/string.po

@@ -648,7 +648,7 @@ msgstr "``'x'``"
 msgid ""
 "Hex format. Outputs the number in base 16, using lower-case letters for the "
 "digits above 9."
-msgstr ""
+msgstr "十六進位格式。輸出以 16 為基數的數字，9 以上的數字使用小寫字母。"
 
 #: ../../library/string.rst:481
 msgid "``'X'``"
@@ -660,6 +660,8 @@ msgid ""
 "digits above 9. In case ``'#'`` is specified, the prefix ``'0x'`` will be "
 "upper-cased to ``'0X'`` as well."
 msgstr ""
+"十六進位格式。輸出以 16 為基數的數字，9 以上的數字使用大寫字母。如果指定了"
+"``'#'``，則前綴 ``'0x'`` 也會被轉成大寫的 ``'0X'``。"
 
 #: ../../library/string.rst:486 ../../library/string.rst:570
 msgid "``'n'``"