diff --git a/Gemfile b/Gemfile
index ffd651e67..48c39c836 100644
--- a/Gemfile
+++ b/Gemfile
@@ -68,6 +68,7 @@ gem "pagy"
 gem "rails-settings-cached"
 gem "tzinfo-data", platforms: %i[windows jruby]
 gem "csv"
+gem "rchardet" # Character encoding detection
 gem "redcarpet"
 gem "stripe"
 gem "plaid"
diff --git a/Gemfile.lock b/Gemfile.lock
index 86435af42..39940bbd9 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -528,6 +528,7 @@ GEM
       ffi (~> 1.0)
     rbs (3.9.4)
       logger
+    rchardet (1.10.0)
     rdoc (6.14.2)
       erb
       psych (>= 4.0.0)
@@ -802,6 +803,7 @@ DEPENDENCIES
   rack-mini-profiler
   rails (~> 7.2.2)
   rails-settings-cached
+  rchardet
   redcarpet
   redis (~> 5.4)
   rotp (~> 6.3)
diff --git a/app/models/import.rb b/app/models/import.rb
index 05b426573..1d288c480 100644
--- a/app/models/import.rb
+++ b/app/models/import.rb
@@ -22,6 +22,7 @@ class Import < ApplicationRecord
   belongs_to :account, optional: true
 
   before_validation :set_default_number_format
+  before_validation :ensure_utf8_encoding
 
   scope :ordered, -> { order(created_at: :desc) }
 
@@ -294,6 +295,68 @@ class Import < ApplicationRecord
       self.number_format ||= "1,234.56" # Default to US/UK format
     end
 
+    # Common encodings to try when UTF-8 detection fails
+    # Windows-1250 is prioritized for Central/Eastern European languages
+    COMMON_ENCODINGS = [ "Windows-1250", "Windows-1252", "ISO-8859-1", "ISO-8859-2" ].freeze
+
+    def ensure_utf8_encoding
+      # Handle nil or empty string first (before checking if changed)
+      return if raw_file_str.nil? || raw_file_str.bytesize == 0
+
+      # Only process if the attribute was changed
+      # Use will_save_change_to_attribute? which is safer for binary data
+      return unless will_save_change_to_raw_file_str?
+
+      # If already valid UTF-8, nothing to do
+      begin
+        if raw_file_str.encoding == Encoding::UTF_8 && raw_file_str.valid_encoding?
+          return
+        end
+      rescue ArgumentError
+        # raw_file_str might have invalid encoding, continue to detection
+      end
+
+      # Detect encoding using rchardet
+      begin
+        require "rchardet"
+        detection = CharDet.detect(raw_file_str)
+        detected_encoding = detection["encoding"]
+        confidence = detection["confidence"]
+
+        # Only convert if we have reasonable confidence in the detection
+        if detected_encoding && confidence > 0.75
+          # Force encoding and convert to UTF-8
+          self.raw_file_str = raw_file_str.force_encoding(detected_encoding).encode("UTF-8", invalid: :replace, undef: :replace)
+        else
+          # Fallback: try common encodings
+          try_common_encodings
+        end
+      rescue LoadError
+        # rchardet not available, fallback to trying common encodings
+        try_common_encodings
+      rescue ArgumentError, Encoding::CompatibilityError => e
+        # Handle encoding errors by falling back to common encodings
+        try_common_encodings
+      end
+    end
+
+    def try_common_encodings
+      COMMON_ENCODINGS.each do |encoding|
+        begin
+          test = raw_file_str.dup.force_encoding(encoding)
+          if test.valid_encoding?
+            self.raw_file_str = test.encode("UTF-8", invalid: :replace, undef: :replace)
+            return
+          end
+        rescue Encoding::InvalidByteSequenceError, Encoding::UndefinedConversionError
+          next
+        end
+      end
+
+      # If nothing worked, force UTF-8 and replace invalid bytes
+      self.raw_file_str = raw_file_str.force_encoding("UTF-8").scrub("?")
+    end
+
     def account_belongs_to_family
       return if account.nil?
       return if account.family_id == family_id
diff --git a/test/fixtures/files/imports/windows1250.csv b/test/fixtures/files/imports/windows1250.csv
new file mode 100644
index 000000000..def36e8e3
--- /dev/null
+++ b/test/fixtures/files/imports/windows1250.csv
@@ -0,0 +1,4 @@
+Date,Name,Amount,Category,Tags,Account,Notes
+2024-01-01,Sklep spożywczy,-50.00,Żywność,Zakupy,Konto główne,Zakupy w sklepie
+2024-01-02,Kawiarnia Café,-15.50,Jedzenie,Kawa|Śniadanie,Karta kredytowa,Poranna kawa
+2024-01-03,Stacja benzynowa,-120.00,Transport,Paliwo|Samochód,Konto główne,Tankowanie auta
diff --git a/test/models/import_encoding_test.rb b/test/models/import_encoding_test.rb
new file mode 100644
index 000000000..0052e8dfc
--- /dev/null
+++ b/test/models/import_encoding_test.rb
@@ -0,0 +1,74 @@
+require "test_helper"
+
+class ImportEncodingTest < ActiveSupport::TestCase
+  setup do
+    @family = families(:dylan_family)
+    @account = accounts(:depository)
+  end
+
+  test "successfully imports Windows-1250 encoded CSV" do
+    # Test that Windows-1250 encoded files are properly converted to UTF-8
+    file_path = Rails.root.join("test/fixtures/files/imports/windows1250.csv")
+    csv_content = File.binread(file_path)
+
+    # Verify the file is not UTF-8
+    assert_equal Encoding::ASCII_8BIT, csv_content.encoding
+    refute csv_content.force_encoding("UTF-8").valid_encoding?, "Test file should not be valid UTF-8"
+
+    import = @family.imports.create!(
+      type: "TransactionImport",
+      account: @account,
+      date_format: "%Y-%m-%d",
+      date_col_label: "Date",
+      amount_col_label: "Amount",
+      name_col_label: "Name",
+      category_col_label: "Category",
+      tags_col_label: "Tags",
+      account_col_label: "Account",
+      notes_col_label: "Notes",
+      signage_convention: "inflows_negative",
+      amount_type_strategy: "signed_amount"
+    )
+
+    # With encoding detection, the import should succeed
+    assert_nothing_raised do
+      import.update!(raw_file_str: csv_content)
+    end
+
+    # Verify the raw_file_str was converted to UTF-8
+    assert_equal Encoding::UTF_8, import.raw_file_str.encoding
+    assert import.raw_file_str.valid_encoding?, "Converted string should be valid UTF-8"
+
+    # Verify we can generate rows from the CSV
+    assert_nothing_raised do
+      import.generate_rows_from_csv
+    end
+
+    # Verify that rows were created
+    import.reload
+    assert import.rows_count > 0, "Expected rows to be created from Windows-1250 CSV"
+    assert_equal 3, import.rows_count, "Expected 3 data rows"
+
+    # Verify Polish characters were preserved correctly
+    first_row = import.rows.first
+    assert_not_nil first_row, "Expected first row to exist"
+    assert_includes first_row.name, "spoĹĽywczy", "Polish characters should be preserved"
+  end
+
+  test "handles UTF-8 files without modification" do
+    # Test that valid UTF-8 files are not modified
+    file_path = Rails.root.join("test/fixtures/files/imports/transactions.csv")
+    csv_content = File.read(file_path, encoding: "UTF-8")
+
+    import = @family.imports.create!(
+      type: "TransactionImport",
+      account: @account,
+      date_format: "%Y-%m-%d",
+      raw_file_str: csv_content
+    )
+
+    # UTF-8 content should remain unchanged
+    assert_equal Encoding::UTF_8, import.raw_file_str.encoding
+    assert import.raw_file_str.valid_encoding?
+  end
+end