Locale.Message: Refactor test

* Check if ja_JP.UTF-8 is available before running each test

test/Locale/Message.vimspec

@@ -5,6 +5,12 @@ let s:text_path = 'test/Locale/MessageText/%s.txt'
 Describe Locale.Message
  Before all
  let M = vital#vital#new().import('Locale.Message')
+ try
+ language message ja_JP.UTF-8
+ let ja_available = 1
+ catch /^Vim\%((\a\+)\)\=:E197/
+ let ja_available = 0
+ endtry
  End
 
  Before each
@@ -13,17 +19,17 @@ Describe Locale.Message
 
  Describe .get_lang()
  It returns current language of message
- try
+ if ja_available
  language message ja_JP.UTF-8
  Assert Equals(M.get_lang(), 'ja')
- catch /^Vim\%((\a\+)\)\=:E197/
+ else
  try
  language message en_US.UTF-8
  Assert Equals(M.get_lang(), 'en')
  catch /^Vim\%((\a\+)\)\=:E197/
  Skip Need ja_JP.UTF-8 or en_US.UTF-8 in your system locale
  endtry
- endtry
+ endif
  End
  It returns 'en' if current language is 'C'
  language message C
@@ -41,17 +47,17 @@ Describe Locale.Message
 
  Describe .get()
  Before each
- try
+ if ja_available
  language message ja_JP.UTF-8
  let self.m = M.new(s:text_path)
- catch /^Vim\%((\a\+)\)\=:E197/
+ else
  try
  language message en_US.UTF-8
  let self.m = M.new(s:text_path)
  catch /^Vim\%((\a\+)\)\=:E197/
  Skip Need ja_JP.UTF-8 or en_US.UTF-8 in your system locale
  endtry
- endtry
+ endif
  End
  It returns translated text if it exists
  if M.get_lang() == 'ja'
@@ -67,17 +73,17 @@ Describe Locale.Message
 
  Describe ._()
  Before each
- try
+ if ja_available
  language message ja_JP.UTF-8
  let self.m = M.new(s:text_path)
- catch /^Vim\%((\a\+)\)\=:E197/
+ else
  try
  language message en_US.UTF-8
  let self.m = M.new(s:text_path)
  catch /^Vim\%((\a\+)\)\=:E197/
  Skip Need ja_JP.UTF-8 or en_US.UTF-8 in your system locale
  endtry
- endtry
+ endif
  End
  It can use like `get()`
  if M.get_lang() == 'ja'