Symptom:

With pango-libthai engine [1] installed, and Bug #355435 fixed, GtkTextView now moves caret word-wise properly through Thai text, but only for the last chunk after the last space. For the text before that, it still moves as if the text were English (that is, words are delimited by spaces).

Note that there is no such error in GtkEntry.

Cause:

GtkTextView relies on pango_get_log_attrs() when getting logical attributes. But a loop within the function just takes the engine from next range to calculate current range:

>  while (pos != end)
>     {
>       ...
>       script = pango_script_for_unichar (g_utf8_get_char (pos));
>       analysis.lang_engine =
>         (PangoEngineLang*) pango_map_get_engine (lang_map, script);
>   
>       if (range_engine != analysis.lang_engine)
>         {
>           /* Engine has changed; do the breaking for the current range,
>            * then start a new range.
>            */
>           pango_break (range_start,
>                        pos - range_start,
>                        &analysis,
>                        log_attrs + chars_broken,
>                        attrs_len - chars_broken);

Here, analysis.lang_engine already holds the engine for the next range. So, it breaks previous range with a different engine.

>           ...
>           range_engine = analysis.lang_engine;
>           ...
>         }
>       ...
>     
>       pos = g_utf8_next_char (pos);
>     }

[1] http://libthai.sourceforge.net/