EDIT: specs and translation updated

config/locales/server.en.yml

@@ -1815,7 +1815,7 @@ en:
     min_trust_to_post_embedded_media: "The minimum trust level required to embed media items in a post"
     min_trust_level_to_allow_profile_background: "The minimum trust level required to upload a profile background"
     min_trust_level_to_allow_user_card_background: "The minimum trust level required to upload a user card background"
-    min_trust_level_to_allow_invite: "The minimum trust level required to allow invite"
+    min_trust_level_to_allow_invite: "The minimum trust level required to invite users"
     allowed_link_domains: "Domains that users may link to even if they don't have the appropriate trust level to post links"
 
     newuser_max_links: "How many links a new user can add to a post."

spec/components/guardian_spec.rb

@@ -625,7 +625,7 @@ describe Guardian do
     end
 
     describe "private messages" do
-      SiteSetting.min_trust_level_to_allow_invite = 2
+      fab!(:user) { Fabricate(:user, trust_level: TrustLevel[2]) }
       fab!(:user) { Fabricate(:user, trust_level: SiteSetting.min_trust_level_to_allow_invite) }
       fab!(:pm) { Fabricate(:private_message_topic, user: user) }
 
@@ -650,9 +650,11 @@ describe Guardian do
       context "when private messages are enabled" do
         before do
           SiteSetting.enable_personal_messages = true
+          SiteSetting.min_trust_level_to_allow_invite = 2
         end
 
         it "returns true if user has sufficient trust level" do
+          user.trust_level = 2
           expect(Guardian.new(user).can_invite_to?(pm)).to be_truthy
         end