diff --git a/src/common/stringutils.cpp b/src/common/stringutils.cpp
index f52c3d04..02624d19 100644
--- a/src/common/stringutils.cpp
+++ b/src/common/stringutils.cpp
@@ -236,3 +236,71 @@ bool StrUtils::isUtf8ContinuationByte(char c)
 {
     return (c & 0b1100'0000) == 0b1000'0000;
 }
+
+std::string StrUtils::ToLower(const std::string& text)
+{
+    std::string result;
+
+    for (size_t i = 0; i < text.size();)
+    {
+        std::mbstate_t state = {};
+        wchar_t ch;
+
+        int len = std::mbrtowc(&ch, text.data() + i, text.size() - i, &state);
+
+        if (len == -1) throw std::invalid_argument("Invalid character");
+
+        if (len == 0) len = 1;
+
+        ch = std::towlower(ch);
+
+        char buffer[8];
+
+        state = {};
+        size_t count = std::wcrtomb(buffer, ch, &state);
+
+        if (count == -1) throw std::invalid_argument("Invalid character");
+
+        if (count == 0) count = 1;
+
+        result.append(buffer, count);
+
+        i += len;
+    }
+
+    return result;
+}
+
+std::string StrUtils::ToUpper(const std::string& text)
+{
+    std::string result;
+
+    for (size_t i = 0; i < text.size();)
+    {
+        std::mbstate_t state = {};
+        wchar_t ch;
+
+        size_t len = std::mbrtowc(&ch, text.data() + i, text.size() - i, &state);
+
+        if (len == -1) throw std::invalid_argument("Invalid character");
+
+        if (len == 0) len = 1;
+
+        ch = std::towupper(ch);
+
+        char buffer[8];
+
+        state = {};
+        size_t count = std::wcrtomb(buffer, ch, &state);
+
+        if (count == -1) throw std::invalid_argument("Invalid character");
+        
+        if (count == 0) count = 1;
+
+        result.append(buffer, count);
+
+        i += len;
+    }
+
+    return result;
+}
diff --git a/src/common/stringutils.h b/src/common/stringutils.h
index 63e10698..fc19cd26 100644
--- a/src/common/stringutils.h
+++ b/src/common/stringutils.h
@@ -98,5 +98,10 @@ std::size_t Utf8StringLength(const std::string &str);
 //! Returns true if char is continuation UTF-8 byte
 bool isUtf8ContinuationByte(char c);
 
-} // namespace StrUtil
+//! Returns the string with characters converted to lower case when possible
+std::string ToLower(const std::string& text);
 
+//! Returns the string with characters converted to upper case when possible
+std::string ToUpper(const std::string& text);
+
+} // namespace StrUtil
diff --git a/test/unit/CMakeLists.txt b/test/unit/CMakeLists.txt
index 8b7792c2..2ddbd3a5 100644
--- a/test/unit/CMakeLists.txt
+++ b/test/unit/CMakeLists.txt
@@ -31,10 +31,16 @@ target_include_directories(colobot_ut PRIVATE
     ${COLOBOT_LOCAL_INCLUDES}
 )
 
+if(MSVC)
+    target_compile_options(colobot_ut PRIVATE /utf-8)
+endif()
+
 target_link_libraries(colobot_ut PRIVATE GTest::GTest hippomocks colobotbase)
 
 gtest_discover_tests(colobot_ut
-    WORKING_DIRECTORY ${CMAKE_RUNTIME_OUTPUT_DIRECTORY})
+    WORKING_DIRECTORY ${CMAKE_RUNTIME_OUTPUT_DIRECTORY}
+    DISCOVERY_MODE PRE_TEST
+)
 
 # GoogleTest isn't compatible with -Wsuggest-override -Werror:
 # see https://github.com/google/googletest/issues/1063
diff --git a/test/unit/common/stringutils_test.cpp b/test/unit/common/stringutils_test.cpp
index 9411bdb9..52dbcc86 100644
--- a/test/unit/common/stringutils_test.cpp
+++ b/test/unit/common/stringutils_test.cpp
@@ -32,7 +32,7 @@ TEST(StringUtilTests, ReplaceShortToLong)
 
     std::string expected = "Test [0987654], [0987654], [0987654][0987654] Test";
 
-    EXPECT_TRUE(result == expected);
+    EXPECT_EQ(result, expected);
 }
 
 TEST(StringUtilTests, ReplaceLongToShort)
@@ -43,7 +43,7 @@ TEST(StringUtilTests, ReplaceLongToShort)
 
     std::string expected = "Test [64], [64], [64][64] Test";
 
-    EXPECT_TRUE(result == expected);
+    EXPECT_EQ(result, expected);
 }
 
 TEST(StringUtilTests, ReplaceSameLength)
@@ -54,7 +54,29 @@ TEST(StringUtilTests, ReplaceSameLength)
 
     std::string expected = "Test [432], [432], [432][432] Test";
 
-    EXPECT_TRUE(result == expected);
+    EXPECT_EQ(result, expected);
+}
+
+TEST(StringUtilTests, ToLowerTest)
+{
+    std::string text = u8",./;AaBbĄąĘę";
+
+    auto result = StrUtils::ToLower(text);
+
+    std::string expected = u8",./;aabbąąęę";
+
+    EXPECT_EQ(result, expected);
+}
+
+TEST(StringUtilTests, ToUpperTest)
+{
+    std::string text = u8",./;AaBbĄąĘę";
+
+    auto result = StrUtils::ToUpper(text);
+
+    std::string expected = u8",./;AABBĄĄĘĘ";
+
+    EXPECT_EQ(result, expected);
 }
 
 } // namespace StringUtils
diff --git a/test/unit/main.cpp b/test/unit/main.cpp
index bc171b16..7741d3eb 100644
--- a/test/unit/main.cpp
+++ b/test/unit/main.cpp
@@ -29,6 +29,8 @@ int main(int argc, char* argv[])
 
     ::testing::InitGoogleTest(&argc, argv);
 
+    std::setlocale(LC_ALL, "en_US.UTF-8");
+
     // parse arguments not removed by InitGoogleTest
     for (int i = 1; i < argc; ++i)
     {