diff --git a/lib/prism/i18n/backend.rb b/lib/prism/i18n/backend.rb
new file mode 100644
index 0000000..896e30d
--- /dev/null
+++ b/lib/prism/i18n/backend.rb
@@ -0,0 +1,68 @@
+module Prism
+  module I18n
+    # Holds translations for every locale as a nested Hash, keyed by symbol
+    # at every level ("posts.title" -> { posts: { title: "..." } }).
+    # Loaded from plain JSON files (no YAML/psych dependency - this build
+    # of Ruby has neither) or stored programmatically.
+    class Backend
+      def initialize
+        @translations = {}
+      end
+
+      def store_translations(locale, data)
+        locale = locale.to_sym
+        @translations[locale] ||= {}
+        deep_merge!(@translations[locale], symbolize(data))
+      end
+
+      def load_file(path)
+        locale = File.basename(path, '.*').to_sym
+        data = JSON.parse(File.read(path))
+        store_translations(locale, data)
+        locale
+      end
+
+      def lookup(locale, key)
+        segments = key.to_s.split('.').map(&:to_sym)
+        root = @translations[locale.to_sym]
+        return nil unless root
+        segments.reduce(root) do |node, segment|
+          return nil unless node.is_a?(Hash)
+          node[segment]
+        end
+      end
+
+      def locales
+        @translations.keys
+      end
+
+      def clear!
+        @translations = {}
+      end
+
+      private
+
+      def symbolize(value)
+        case value
+        when Hash
+          value.each_with_object({}) { |(key, nested), acc| acc[key.to_sym] = symbolize(nested) }
+        when Array
+          value.map { |entry| symbolize(entry) }
+        else
+          value
+        end
+      end
+
+      def deep_merge!(target, source)
+        source.each do |key, value|
+          if value.is_a?(Hash) && target[key].is_a?(Hash)
+            deep_merge!(target[key], value)
+          else
+            target[key] = value
+          end
+        end
+        target
+      end
+    end
+  end
+end
diff --git a/lib/prism/i18n/translator.rb b/lib/prism/i18n/translator.rb
new file mode 100644
index 0000000..9bb2535
--- /dev/null
+++ b/lib/prism/i18n/translator.rb
@@ -0,0 +1,84 @@
+module Prism
+  module I18n
+    # Resolves a translate/localize call against a Backend: locale fallback
+    # chains, %{name} interpolation, and English-style count pluralization
+    # (:zero/:one/:other keys, falling back to :other).
+    class Translator
+      MissingTranslationError = Class.new(StandardError)
+      MissingInterpolationError = Class.new(StandardError)
+
+      DEFAULT_TIME_FORMAT = '%Y-%m-%d %H:%M:%S'
+      DEFAULT_DATE_FORMAT = '%Y-%m-%d'
+
+      def initialize(backend, default_locale: :en, fallbacks: {})
+        @backend = backend
+        @default_locale = default_locale.to_sym
+        @fallbacks = fallbacks.transform_keys(&:to_sym).transform_values { |chain| Array(chain).map(&:to_sym) }
+      end
+
+      def translate(key, locale: @default_locale, count: nil, default: nil, **interpolations)
+        entry = resolve(key, locale)
+        if entry.nil?
+          return interpolate(default, count: count, **interpolations) unless default.nil?
+          raise MissingTranslationError, "translation missing: #{locale}.#{key}"
+        end
+        entry = pluralize(entry, count) if entry.is_a?(Hash) && !count.nil?
+        interpolate(entry, count: count, **interpolations)
+      end
+      alias_method :t, :translate
+
+      def localize(value, locale: @default_locale, format: :default)
+        pattern = resolve("#{scope_for(value)}.formats.#{format}", locale) ||
+                  default_format_for(value)
+        value.strftime(pattern)
+      end
+      alias_method :l, :localize
+
+      private
+
+      def resolve(key, locale)
+        chain_for(locale).each do |candidate|
+          value = @backend.lookup(candidate, key)
+          return value unless value.nil?
+        end
+        nil
+      end
+
+      def chain_for(locale)
+        locale = locale.to_sym
+        chain = [locale] + @fallbacks.fetch(locale, [])
+        chain << @default_locale unless chain.include?(@default_locale)
+        chain.uniq
+      end
+
+      def pluralize(rules, count)
+        key = plural_key(count, rules)
+        rules[key] || rules[:other] || rules.values.first
+      end
+
+      def plural_key(count, rules)
+        return :zero if count == 0 && rules.key?(:zero)
+        return :one if count == 1
+        :other
+      end
+
+      def interpolate(text, count: nil, **interpolations)
+        return text unless text.is_a?(String)
+        values = interpolations.dup
+        values[:count] = count unless count.nil?
+        text.gsub(/%\{(\w+)\}/) do
+          key = Regexp.last_match(1).to_sym
+          values.fetch(key) { raise MissingInterpolationError, "missing interpolation argument #{key.inspect} for #{text.inspect}" }.to_s
+        end
+      end
+
+      def scope_for(value)
+        value.is_a?(Time) ? 'time' : 'date'
+      end
+
+      def default_format_for(value)
+        value.is_a?(Time) ? DEFAULT_TIME_FORMAT : DEFAULT_DATE_FORMAT
+      end
+    end
+  end
+end