Added tests for four locales and three locales.

The four locales include 2 language and 2 regional locales.

The three locales include 2 language and 1 regional locales.

The tests include testing for fall-backs with default locale, differing
between language and regional locales. The tests also cover all
combinations of whether a string is specified in the locale and whether
there are differences in the locale. Here are the 25 combinations for
four locales:
 1 - different between en and en-GB, different between zh and zh-TW
 2 - same in en and en-GB,           different between zh and zh-TW
 3 - in en only,                     different between zh and zh-TW
 4 - in en-GB only,                  different between zh and zh-TW
 5 - not in en and en-GB,            different between zh and zh-TW
 6 - different between en and en-GB, same in zh and zh-TW
 7 - same in en and en-GB,           same in zh and zh-TW
 8 - in en only,                     same in zh and zh-TW
 9 - in en-GB only,                  same in zh and zh-TW
10 - not in en and en-GB,            same in zh and zh-TW
11 - different between en and en-GB, in zh only
12 - same in en and en-GB,           in zh only
13 - in en only,                     in zh only
14 - in en-GB only,                  in zh only
15 - not in en and en-GB,            in zh only
16 - different between en and en-GB, in zh-TW only
17 - same in en and en-GB,           in zh-TW only
18 - in en only,                     in zh-TW only
19 - in en-GB only,                  in zh-TW only
20 - not in en and en-GB,            in zh-TW only
21 - different between en and en-GB, not in zh and zh-TW
22 - same in en and en-GB,           not in zh and zh-TW
23 - in en only,                     not in zh and zh-TW
24 - in en-GB only,                  not in zh and zh-TW
25 - not in en and en-GB,            not in zh and zh-TW

The tests for three locales were derived from that of the four
locales, consisting of a subset of 10 combinations:
 6 - different between en and en-GB, in zh
 7 - same in en and en-GB,           in zh
 8 - in en only,                     in zh
 9 - in en-GB only,                  in zh
10 - not in en and en-GB,            in zh
16 - different between en and en-GB, not in zh
17 - same in en and en-GB,           not in zh
18 - in en only,                     not in zh
19 - in en-GB only,                  not in zh
20 - not in en and en-GB,            not in zh