If language needs to be reset at the end of footnotes or floats

then do reset it only after footnotes or floats. \selectlanguage at
the end of environments might produce spurious vertical space
(see https://marc.info/?l=lyx-devel&m=168872369617866)

src/OutputParams.h

@@ -291,6 +291,10 @@ public:
 	 */
 	bool inInclude = false;
 
+	/** Whether we are inside a footnote. 
+	 */
+	bool inFootnote = false;
+
 	/** Whether a btUnit (for multiple biblographies) is open.
 	 */
 	mutable bool openbtUnit = false;

src/insets/InsetFoot.cpp

@@ -111,6 +111,14 @@ docstring InsetFoot::toolTip(BufferView const & bv, int x, int y) const
 }
 
 
+void InsetFoot::latex(otexstream & os, OutputParams const & runparams_in) const
+{
+	OutputParams runparams(runparams_in);
+	runparams.inFootnote = true;
+	InsetText::latex(os, runparams);
+}
+
+
 int InsetFoot::plaintext(odocstringstream & os,
         OutputParams const & runparams, size_t max_length) const
 {

src/insets/InsetFoot.h

@@ -32,6 +32,8 @@ private:
 	///
 	docstring layoutName() const override;
 	///
+	void latex(otexstream &, OutputParams const &) const override;
+	///
 	int plaintext(odocstringstream & ods, OutputParams const & op,
 	              size_t max_length = INT_MAX) const override;
 	///

src/output_latex.cpp

@@ -1298,13 +1298,15 @@ void TeXOnePar(Buffer const & buf,
 	if (localswitch_needed
 	    || (intitle_command && using_begin_end)
 	    || closing_rtl_ltr_environment
-	    || (((runparams.isLastPar && !runparams.inbranch) || close_lang_switch)
-	        && (par_lang != outer_lang || (using_begin_end
-						&& style.isEnvironment()
-						&& par_lang != nextpar_lang)))) {
 		// Since \selectlanguage write the language to the aux file,
 		// we need to reset the language at the end of footnote or
 		// float.
+	    || (((runparams.isLastPar
+		  && (using_begin_end || runparams.inFloat != OutputParams::NONFLOAT || runparams.inFootnote))
+		 || close_lang_switch)
+	        && (par_lang != outer_lang || (using_begin_end
+						&& style.isEnvironment()
+						&& par_lang != nextpar_lang)))) {
 
 		if (!localswitch && (pending_newline || close_lang_switch))
 			os << '\n';