Fix plurals on some GUI strings (#12681)

# Description
Some terms were singular and should be plural, and vice-versa.

src/libslic3r/PrintConfig.cpp

@@ -3973,7 +3973,7 @@ void PrintConfigDef::init_fff_params()
     def->enum_labels.push_back(L("No ironing"));
     def->enum_labels.push_back(L("Top surfaces"));
     def->enum_labels.push_back(L("Topmost surface"));
-    def->enum_labels.push_back(L("All solid layer"));
+    def->enum_labels.push_back(L("All solid layers"));
     def->mode = comAdvanced;
     def->set_default_value(new ConfigOptionEnum<IroningType>(IroningType::NoIroning));
 
@@ -4555,7 +4555,7 @@ void PrintConfigDef::init_fff_params()
     def->set_default_value(new ConfigOptionFloat(0.));
 
     def = this->add("detect_overhang_wall", coBool);
-    def->label = L("Detect overhang wall");
+    def->label = L("Detect overhang walls");
     def->category = L("Quality");
     def->tooltip = L("Detect the overhang percentage relative to line width and use different speed to print. "
                      "For 100%% overhang, bridge speed is used.");
@@ -5305,7 +5305,7 @@ void PrintConfigDef::init_fff_params()
     def = this->add("minimum_sparse_infill_area", coFloat);
     def->label = L("Minimum sparse infill threshold");
     def->category = L("Strength");
-    def->tooltip = L("Sparse infill area which is smaller than threshold value is replaced by internal solid infill.");
+    def->tooltip = L("Sparse infill areas smaller than this threshold value are replaced by internal solid infill.");
     def->sidetext = L(u8"mm²");	// square milimeters, CIS languages need translation
     def->min = 0;
     def->mode = comAdvanced;
@@ -6146,10 +6146,10 @@ void PrintConfigDef::init_fff_params()
     def->set_default_value(new ConfigOptionPoints{});
 
     def = this->add("detect_thin_wall", coBool);
-    def->label = L("Detect thin wall");
+    def->label = L("Detect thin walls");
     def->category = L("Strength");
-    def->tooltip = L("Detect thin wall which can't contain two line width. And use single line to print. "
-                     "Maybe printed not very well, because it's not closed loop.");
+    def->tooltip = L("Detect thin walls which can't contain two line widths, and use single line to print. "
+                     "Maybe not printed very well, because it's not a closed loop.");
     def->mode = comAdvanced;
     def->set_default_value(new ConfigOptionBool(false));
 
@@ -6760,7 +6760,7 @@ void PrintConfigDef::init_fff_params()
     }
 
     def = this->add("detect_narrow_internal_solid_infill", coBool);
-    def->label = L("Detect narrow internal solid infill");
+    def->label = L("Detect narrow internal solid infills");
     def->category = L("Strength");
     def->tooltip = L("This option will auto-detect narrow internal solid infill areas. "
                      "If enabled, the concentric pattern will be used for the area to speed up printing. "

src/slic3r/GUI/MainFrame.cpp

@@ -2485,7 +2485,7 @@ static wxMenu* generate_help_menu()
     //        //TODO
     //    });
     // Check New Version
-    append_menu_item(helpMenu, wxID_ANY, _L("Check for Update"), _L("Check for Update"),
+    append_menu_item(helpMenu, wxID_ANY, _L("Check for Updates"), _L("Check for Updates"),
         [](wxCommandEvent&) {
             wxGetApp().check_new_version_sf(true, 1);
         }, "", nullptr, []() {

src/slic3r/GUI/PrintOptionsDialog.cpp

@@ -639,7 +639,7 @@ wxBoxSizer* PrintOptionsDialog::create_settings_group(wxWindow* parent)
     ai_refine_sizer->Add(line_sizer, 0, wxEXPAND | wxLEFT | wxRIGHT, FromDIP(18));
 
     line_sizer = new wxBoxSizer(wxHORIZONTAL);
-    text_spaghetti_detection_caption0 = new Label(ai_refine_panel, _L("Detect spaghetti failure(scattered lose filament)."));
+    text_spaghetti_detection_caption0 = new Label(ai_refine_panel, _L("Detect spaghetti failures (scattered lose filament)."));
     text_spaghetti_detection_caption0->SetFont(Label::Body_12);
     text_spaghetti_detection_caption0->SetForegroundColour(STATIC_TEXT_CAPTION_COL);
     text_spaghetti_detection_caption0->Wrap(-1);

src/slic3r/GUI/UnsavedChangesDialog.cpp

@@ -1668,7 +1668,7 @@ void UnsavedChangesDialog::update_tree(Preset::Type type, PresetCollection* pres
         // process changes of extruders count
         if (type == Preset::TYPE_PRINTER && old_pt == ptFFF &&
             old_config.opt<ConfigOptionFloats>("nozzle_diameter")->values.size() != new_config.opt<ConfigOptionFloats>("nozzle_diameter")->values.size()) {
-            wxString local_label = _L("Extruders count");
+            wxString local_label = _L("Extruder count");
             wxString old_val = from_u8((boost::format("%1%") % old_config.opt<ConfigOptionFloats>("nozzle_diameter")->values.size()).str());
             wxString new_val = from_u8((boost::format("%1%") % new_config.opt<ConfigOptionFloats>("nozzle_diameter")->values.size()).str());
 
@@ -2228,7 +2228,7 @@ void DiffPresetDialog::update_tree()
         // process changes of extruders count
         if (type == Preset::TYPE_PRINTER && left_pt == ptFFF &&
             left_config.opt<ConfigOptionStrings>("extruder_colour")->values.size() != right_congig.opt<ConfigOptionStrings>("extruder_colour")->values.size()) {
-            wxString local_label = _L("Extruders count");
+            wxString local_label = _L("Extruder count");
             wxString left_val = from_u8((boost::format("%1%") % left_config.opt<ConfigOptionStrings>("extruder_colour")->values.size()).str());
             wxString right_val = from_u8((boost::format("%1%") % right_congig.opt<ConfigOptionStrings>("extruder_colour")->values.size()).str());