Some Asian langagues allow to wrap text at any position

This is hardcoded for now for simplicity and to allow backporting to
2.3.

The behavior is unchanged for all languages but Chinese, Japanese or
Korean.

Fixes part of bug #10299.

(cherry picked from commit 26c2811cc4)

src/Row.cpp

@@ -19,6 +19,7 @@
 #include "Row.h"
 
 #include "DocIterator.h"
+#include "Language.h"
 
 #include "frontends/FontMetrics.h"
 
@@ -473,7 +474,25 @@ bool Row::shortenIfNeeded(pos_type const keep, int const w, int const next_width
 		// make a copy of the element to work on it.
 		Element brk = *cit_brk;
 		wid_brk -= brk.dim.wid;
-		if (brk.countSeparators() == 0 || brk.pos < keep)
+		/*
+		 * Some Asian languages split lines anywhere (no notion of
+		 * word). It seems that QTextLayout is not aware of this fact.
+		 * See for reference:
+		 *    https://en.wikipedia.org/wiki/Line_breaking_rules_in_East_Asian_languages
+		 *
+		 * FIXME: Something shall be done about characters which are
+		 * not allowed at the beginning or end of line.
+		 *
+		 * FIXME: hardcoding languages is bad. Put this information in
+		 * `languages' file.
+		*/
+		string const lang = brk.font.language()->lang();
+		bool force = lang == "chinese-simplified"
+		             || lang == "chinese-traditional"
+		             || lang == "japanese"
+		             || lang == "korean";
+		// FIXME: is it important to check for separators?
+		if ((!force && brk.countSeparators() == 0) || brk.pos < keep)
 			continue;
 		/* We have found a suitable separable element. This is the common case.
 		 * Try to break it cleanly (at word boundary) at a length that is both
@@ -481,7 +500,7 @@ bool Row::shortenIfNeeded(pos_type const keep, int const w, int const next_width
 		 * - shorter than the natural width of the element, in order to enforce
 		 *   break-up.
 		 */
-		if (brk.breakAt(min(w - wid_brk, brk.dim.wid - 2), false)) {
+		if (brk.breakAt(min(w - wid_brk, brk.dim.wid - 2), force)) {
 			/* if this element originally did not cause a row overflow
 			 * in itself, and the remainder of the row would still be
 			 * too large after breaking, then we will have issues in

status.23x

@@ -61,6 +61,9 @@ What's new
 
 - Improve some icons (bug 11476).
 
+- Improve line breaking of Chinese, Japanese and Korean text. There are still
+  issues, though (bug 10299).
+
 
 * DOCUMENTATION AND LOCALIZATION