In translation phase 6, the multibyte character sequences specified by any sequence of
adjacent character and wide string literal tokens are concatenated into a single multibyte
character sequence. If any of the tokens are wide string literal tokens, the resulting
multibyte character sequence is treated as a wide string literal; otherwise, it is treated as a
character string literal.
Немного устаревшая инфа. Вот с уточнениями из C11:
In translation phase 6, the multibyte character sequences specified by any sequence of
adjacent character and identically-prefixed string literal tokens are concatenated into a
single multibyte character sequence. If any of the tokens has an encoding prefix, the
resulting multibyte character sequence is treated as having the same prefix; otherwise, it
is treated as a character string literal. Whether differently-prefixed wide string literal
tokens can be concatenated and, if so, the treatment of the resulting multibyte character
sequence are implementation-defined.
Ну не особо устаревшая, просто без лишнего. Оно так же и работает, в C11 просто добавили информацию о новых типах литералов, а "" и L"" продолжают неявно конкатенироваться.
Чем отличается россиянин, который пишет код, от замшелого американца, который пишет код? Тем, что он имеет представление в лучшем случае о двух алфавитах, не об одном.