Use local babel language switch in fixed width cells in order to prevent unwanted whitespace

Fixes: #9455

src/insets/Inset.h

@@ -398,6 +398,9 @@ public:
 		{ return true; }
 	/// Is the width forced to some value?
 	virtual bool hasFixedWidth() const { return false; }
+	/// if this inset has paragraphs should they be forced to use a
+	/// local font language switch?
+	virtual bool forceLocalFontSwitch() const { return false; }
 
 	/// Is the content of this inset part of the output document?
 	virtual bool producesOutput() const { return true; }

src/insets/InsetTabular.cpp

@@ -3390,6 +3390,12 @@ bool InsetTableCell::allowParagraphCustomization(idx_type) const
 }
 
 
+bool InsetTableCell::forceLocalFontSwitch() const
+{
+	return isFixedWidth;
+}
+
+
 bool InsetTableCell::getStatus(Cursor & cur, FuncRequest const & cmd,
 	FuncStatus & status) const
 {

src/insets/InsetTabular.h

@@ -115,9 +115,11 @@ private:
 	virtual bool forcePlainLayout(idx_type = 0) const;
 	///
 	virtual bool allowParagraphCustomization(idx_type = 0) const;
+	///
+	virtual bool forceLocalFontSwitch() const;
 	/// Is the width forced to some value?
 	bool hasFixedWidth() const { return isFixedWidth; }
-	/// Can the cell contain several paragraphs? 
+	/// Can the cell contain several paragraphs?
 	/** FIXME this is wrong for multirows, that are limited to one
 	 * paragraph. However, we cannot test for this (see the big
 	 * comment above).

src/insets/InsetText.h

@@ -153,11 +153,14 @@ public:
 	virtual bool allowMultiPar() const { return getLayout().isMultiPar(); }
 	///
 	/// should paragraphs be forced to use the empty layout?
-	virtual bool forcePlainLayout(idx_type = 0) const 
+	virtual bool forcePlainLayout(idx_type = 0) const
 		{ return getLayout().forcePlainLayout(); }
 	/// should the user be allowed to customize alignment, etc.?
-	virtual bool allowParagraphCustomization(idx_type = 0) const 
+	virtual bool allowParagraphCustomization(idx_type = 0) const
 		{ return getLayout().allowParagraphCustomization(); }
+	/// should paragraphs be forced to use a local font language switch?
+	virtual bool forceLocalFontSwitch() const
+		{ return getLayout().forcelocalfontswitch(); }
 
 	/// Update the counters of this inset and of its contents
 	virtual void updateBuffer(ParIterator const &, UpdateType);

src/output_latex.cpp

@@ -672,7 +672,7 @@ void TeXOnePar(Buffer const & buf,
 
 	// In some insets (such as Arguments), we cannot use \selectlanguage
 	bool const localswitch = !use_polyglossia
-		&& text.inset().getLayout().forcelocalfontswitch();
+		&& text.inset().forceLocalFontSwitch();
 	if (localswitch) {
 		lang_begin_command = lyxrc.language_command_local;
 		lang_end_command = "}";