diff --git a/lib/i18n.rb b/lib/i18n.rb
index d3369704..0075a360 100644
--- a/lib/i18n.rb
+++ b/lib/i18n.rb
@@ -331,12 +331,11 @@ def with_locale(tmp_locale = nil)
     # keys are Symbols.
     def normalize_keys(locale, key, scope, separator = nil)
       separator ||= I18n.default_separator
+      locale = locale.to_sym if locale
 
-      [
-        *normalize_key(locale, separator),
-        *normalize_key(scope, separator),
-        *normalize_key(key, separator)
-      ]
+      result = [locale]
+      result.concat(normalize_key(scope, separator)) if scope
+      result.concat(normalize_key(key, separator))
     end
 
     # Returns true when the passed locale, which can be either a String or a
diff --git a/lib/i18n/backend/base.rb b/lib/i18n/backend/base.rb
index 217c3ff0..57756758 100644
--- a/lib/i18n/backend/base.rb
+++ b/lib/i18n/backend/base.rb
@@ -54,7 +54,7 @@ def translate(locale, key, options = EMPTY_HASH)
         end
 
         deep_interpolation = options[:deep_interpolation]
-        values = Utils.except(options, *RESERVED_KEYS)
+        values = Utils.except(options, *RESERVED_KEYS) unless options.empty?
         if values
           entry = if deep_interpolation
             deep_interpolate(locale, entry, values)
@@ -123,7 +123,12 @@ def subtrees?
         # first translation that can be resolved. Otherwise it tries to resolve
         # the translation directly.
         def default(locale, object, subject, options = EMPTY_HASH)
-          options = options.reject { |key, value| key == :default }
+          if options.size == 1 && options.has_key?(:default)
+            options = {}
+          else
+            options = Utils.except(options, :default)
+          end
+
           case subject
           when Array
             subject.each do |item|
diff --git a/lib/i18n/interpolate/ruby.rb b/lib/i18n/interpolate/ruby.rb
index dab8f0ed..bfe484e8 100644
--- a/lib/i18n/interpolate/ruby.rb
+++ b/lib/i18n/interpolate/ruby.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # heavily based on Masao Mutoh's gettext String interpolation extension
 # http://github.com/mutoh/gettext/blob/f6566738b981fe0952548c421042ad1e0cdfb31e/lib/gettext/core_ext/string.rb
 
@@ -10,6 +12,11 @@ module I18n
   INTERPOLATION_PATTERN = Regexp.union(DEFAULT_INTERPOLATION_PATTERNS)
   deprecate_constant :INTERPOLATION_PATTERN
 
+  INTERPOLATION_PATTERNS_CACHE = Hash.new do |hash, patterns|
+    hash[patterns] = Regexp.union(patterns)
+  end
+  private_constant :INTERPOLATION_PATTERNS_CACHE
+
   class << self
     # Return String or raises MissingInterpolationArgument exception.
     # Missing argument's logic is handled by I18n.config.missing_interpolation_argument_handler.
@@ -20,7 +27,8 @@ def interpolate(string, values)
     end
 
     def interpolate_hash(string, values)
-      string.gsub(Regexp.union(config.interpolation_patterns)) do |match|
+      pattern = INTERPOLATION_PATTERNS_CACHE[config.interpolation_patterns]
+      string.gsub(pattern) do |match|
         if match == '%%'
           '%'
         else