Neither names.cfg nor traits.cfg contain relevant WML,

...don't put them in [+units] tags. The scenarios directories don't
contain WML files, don't preprocess them. Don't change the text domain
to itself at each traits macro substitution, do it only once and
benefit from file scoping.

data/game.cfg

@@ -1,8 +1,6 @@
 {themes}
 
-[+units]
-	{traits.cfg}
-[/units]
+{traits.cfg}
 
 {utils.cfg}
 
@@ -11,9 +9,7 @@
 
 {schedules.cfg}
 
-[+units]
-	{names.cfg}
-[/units]
+{names.cfg}
 
 {multiplayer.cfg}
 
@@ -25,7 +21,6 @@
 
 {terrain_generator.cfg}
 
-{~scenarios}
 {campaigns}
 {~campaigns}
 
@@ -1712,6 +1707,4 @@ default=yes
 {scenarios/tutorial}
 #endif
 
-{scenarios}
-
 {scenario-test.cfg}

data/traits.cfg

@@ -1,6 +1,7 @@
+#textdomain wesnoth
+
 #define TRAIT_LOYAL
 	[trait]
-	#textdomain wesnoth
 	id=loyal
 	name= _ "loyal"
 	description= _ "Zero upkeep"
@@ -12,7 +13,6 @@
 
 #define TRAIT_UNDEAD
 	[trait]
-	#textdomain wesnoth
 	id=undead
 	name= _ "undead"
 	description= _ "Immune to poison"
@@ -21,7 +21,6 @@
 
 #define TRAIT_STRONG
 	[trait]
-	#textdomain wesnoth
 	id=strong
 	name= _ "strong"
 		[effect]
@@ -39,7 +38,6 @@
 
 #define TRAIT_DEXTROUS
 	[trait]
-	#textdomain wesnoth
 	id=dextrous
 	name= _ "dextrous"
 		[effect]
@@ -52,7 +50,6 @@
 
 #define TRAIT_QUICK
 	[trait]
-	#textdomain wesnoth
 	id=quick
 	name= _ "quick"
 		[effect]
@@ -69,7 +66,6 @@
 
 #define TRAIT_INTELLIGENT
 	[trait]
-	#textdomain wesnoth
 	id=intelligent
 	name= _ "intelligent"
 		[effect]
@@ -81,7 +77,6 @@
 
 #define TRAIT_RESILIENT
 	[trait]
-	#textdomain wesnoth
 	id=resilient
 	name= _ "resilient"
 		[effect]