diff --git a/compiler2/PredefFunc.cc b/compiler2/PredefFunc.cc
index 71c58cd753491a40cce738d400a159754359a9bc..b4592322e098085afcb52c4a28b46ff304721ef6 100644
--- a/compiler2/PredefFunc.cc
+++ b/compiler2/PredefFunc.cc
@@ -30,6 +30,7 @@
 #include "../common/pattern.hh"
 #include "../common/UnicharPattern.hh"
 #include <iostream>
+#include <locale.h>
 
 // used by regex
 #define ERRMSG_BUFSIZE 512
@@ -607,11 +608,13 @@ namespace Common {
       return new string("not_a_number");
     }
     char str_buf[64];
-    if ( (value > -MAX_DECIMAL_FLOAT && value <= -MIN_DECIMAL_FLOAT)
+    bool f = (value > -MAX_DECIMAL_FLOAT && value <= -MIN_DECIMAL_FLOAT)
       || (value >= MIN_DECIMAL_FLOAT && value <   MAX_DECIMAL_FLOAT)
-      || (value == 0.0))
-      snprintf(str_buf,64,"%f",value);
-    else snprintf(str_buf,64,"%e",value);
+      || (value == 0.0);
+    const char* loc = setlocale(LC_ALL, NULL);
+    setlocale(LC_NUMERIC, "C"); // use default locale for displaying numbers
+    snprintf(str_buf, 64, f ? "%f" : "%e", value);
+    setlocale(LC_NUMERIC, loc);
     return new string(str_buf);
   }
 
diff --git a/core/Addfunc.cc b/core/Addfunc.cc
index 3c7722ebc8e00a13217f8d820e53f14c2be41d11..1952b4326f95193cf34bbdfed420c18b60751bee 100644
--- a/core/Addfunc.cc
+++ b/core/Addfunc.cc
@@ -45,6 +45,7 @@
 #include <string.h>
 #include <sys/types.h>
 #include <regex.h>
+#include <locale.h>
 
 #define ERRMSG_BUFSIZE 512
 
@@ -2876,7 +2877,10 @@ CHARSTRING float2str(double value)
     || (value >= MIN_DECIMAL_FLOAT && value < MAX_DECIMAL_FLOAT);
   // true if decimal representation possible (use %f format)
   char str_buf[64];
+  const char* loc = setlocale(LC_ALL, NULL);
+  setlocale(LC_NUMERIC, "C"); // use default locale for displaying numbers
   int str_len = snprintf(str_buf, sizeof(str_buf), f ? "%f" : "%e", value);
+  setlocale(LC_NUMERIC, loc);
   if (str_len < 0 || str_len >= (int)sizeof(str_buf)) {
     TTCN_error("Internal error: system call snprintf() returned "
       "unexpected status code %d when converting value %g in function "
diff --git a/core/Float.cc b/core/Float.cc
index c9c04d4540647c001f5f5214b5722d9d82b65f18..53f18f3427ceaad1c94c4b43d41bb523af5cefe6 100644
--- a/core/Float.cc
+++ b/core/Float.cc
@@ -25,6 +25,7 @@
 #include <string.h>
 #include <math.h>
 #include <float.h>
+#include <locale.h>
 
 #include "../common/memory.h"
 #include "Float.hh"
@@ -60,17 +61,21 @@ const FLOAT NOT_A_NUMBER((double)PLUS_INFINITY+(double)MINUS_INFINITY);
 
 static inline void log_float(double float_val)
 {
-  if (   (float_val > -MAX_DECIMAL_FLOAT && float_val <= -MIN_DECIMAL_FLOAT)
-      || (float_val >= MIN_DECIMAL_FLOAT && float_val <   MAX_DECIMAL_FLOAT)
-      || (float_val == 0.0))
-    TTCN_Logger::log_event("%f", float_val);
-  else if(float_val==INFINITY)
+  if(float_val==INFINITY)
     TTCN_Logger::log_event_str("infinity");
   else if(float_val==-INFINITY)
     TTCN_Logger::log_event_str("-infinity");
   else if(float_val!=float_val)
     TTCN_Logger::log_event_str("not_a_number");
-  else TTCN_Logger::log_event("%e", float_val);
+  else {
+    boolean f = (float_val > -MAX_DECIMAL_FLOAT && float_val <= -MIN_DECIMAL_FLOAT)
+      || (float_val >= MIN_DECIMAL_FLOAT && float_val <   MAX_DECIMAL_FLOAT)
+      || (float_val == 0.0);
+    const char* loc = setlocale(LC_ALL, NULL);
+    setlocale(LC_NUMERIC, "C"); // use default locale for displaying numbers
+    TTCN_Logger::log_event(f ? "%f" : "%e", float_val);
+    setlocale(LC_NUMERIC, loc);
+  }
 }
 
 // float value class
diff --git a/regression_test/Makefile b/regression_test/Makefile
index 8ab5ba4f2f6499c6011530d4260bc4b05d64aca2..114053ac721078c2a6f8101965d8ea40ef59932f 100644
--- a/regression_test/Makefile
+++ b/regression_test/Makefile
@@ -49,7 +49,8 @@ all_from lazyEval tryCatch text2ttcn json ttcn2json profiler templateOmit \
 customEncoding makefilegen uidChars checkstate hostid templateIstemplatekind \
 selectUnion templateExclusiveRange any_from templatePatternRef indexWithRecofArray \
 connectMapOperTest fuzzy portTranslation ischosen OER functionSubref done \
-nondeterministicDefaultParam predefFunction2 realtime portTranslationCentralStorage
+nondeterministicDefaultParam predefFunction2 realtime portTranslationCentralStorage \
+locale
 
 ifdef DYN
 DIRS += loggerplugin junitlogger 
diff --git a/regression_test/locale/.gitignore b/regression_test/locale/.gitignore
new file mode 100644
index 0000000000000000000000000000000000000000..62c4d845ca0352094c76e27fa7f3bd562e2b7c54
--- /dev/null
+++ b/regression_test/locale/.gitignore
@@ -0,0 +1,6 @@
+locale
+locale.exe
+locale*.cc
+locale*.hh
+compile
+locale*.log
diff --git a/regression_test/locale/Makefile b/regression_test/locale/Makefile
new file mode 100644
index 0000000000000000000000000000000000000000..2c209e8ac1b7ed82b70d7a5761a6abd9db4f2fae
--- /dev/null
+++ b/regression_test/locale/Makefile
@@ -0,0 +1,60 @@
+##############################################################################
+# Copyright (c) 2000-2019 Ericsson Telecom AB
+# All rights reserved. This program and the accompanying materials
+# are made available under the terms of the Eclipse Public License v2.0
+# which accompanies this distribution, and is available at
+# https://www.eclipse.org/org/documents/epl-2.0/EPL-2.0.html
+#
+# Contributors:
+#   Baranyi, Botond
+#
+##############################################################################
+TOPDIR := ..
+include $(TOPDIR)/Makefile.regression
+
+.SUFFIXES: .ttcn .hh
+.PHONY: all clean dep run
+
+TTCN3_LIB = ttcn3$(RT2_SUFFIX)$(DYNAMIC_SUFFIX)
+
+TTCN3_MODULES = locale.ttcn
+
+USER_SOURCES = ext_func.cc
+
+GENERATED_SOURCES = $(TTCN3_MODULES:.ttcn=.cc)
+GENERATED_HEADERS = $(GENERATED_SOURCES:.cc=.hh)
+ifdef CODE_SPLIT
+GENERATED_SOURCES := $(foreach file, $(GENERATED_SOURCES:.cc=), $(addprefix $(file), .cc _seq.cc _set.cc  _seqof.cc _setof.cc _union.cc))
+else ifdef SPLIT_TO_SLICES
+POSTFIXES := $(foreach file, $(SPLIT_TO_SLICES), $(addsuffix $(file), _part_))
+POSTFIXES := $(foreach file, $(POSTFIXES), $(addprefix $(file), .cc))
+GENERATED_SOURCES2 := $(foreach file, $(GENERATED_SOURCES:.cc=), $(addprefix $(file), $(POSTFIXES)))
+GENERATED_SOURCES += $(GENERATED_SOURCES2)
+endif
+
+OBJECTS = $(GENERATED_SOURCES:.cc=.o) $(USER_SOURCES:.cc=.o)
+
+TARGET = locale
+
+all: $(TARGET) ;
+
+$(TARGET): $(GENERATED_SOURCES) $(USER_SOURCES)
+	$(CXX) $(CPPFLAGS) $(CXXFLAGS) $(LDFLAGS) -o $@ $^ -L$(TTCN3_DIR)/lib -l$(TTCN3_LIB) \
+	-L$(OPENSSL_DIR)/lib -lcrypto $($(PLATFORM)_LIBS)
+
+$(GENERATED_SOURCES) $(GENERATED_HEADERS): compile
+	@if [ ! -f $@ ]; then $(RM) compile; $(MAKE) compile; fi
+
+compile: $(TTCN3_MODULES) $(ASN1_MODULES)
+	$(TTCN3_COMPILER) $(COMPILER_FLAGS) $^
+	touch $@
+
+clean distclean:
+	$(RM) $(TARGET) $(OBJECTS) $(GENERATED_HEADERS) \
+	$(GENERATED_SOURCES) compile *.log
+
+dep: $(GENERATED_SOURCES)
+	makedepend $(CPPFLAGS) $(USER_SOURCES) $(GENERATED_SOURCES)
+
+run: $(TARGET) locale.cfg
+	./$^
diff --git a/regression_test/locale/ext_func.cc b/regression_test/locale/ext_func.cc
new file mode 100644
index 0000000000000000000000000000000000000000..ae3f521d41b84bb266c2fe1805efde50745d02cb
--- /dev/null
+++ b/regression_test/locale/ext_func.cc
@@ -0,0 +1,22 @@
+/******************************************************************************
+ * Copyright (c) 2000-2019 Ericsson Telecom AB
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/org/documents/epl-2.0/EPL-2.0.html
+ *
+ * Contributors:
+ *   Baranyi, Botond
+ *
+ ******************************************************************************/
+
+#include <locale.h>
+#include "locale.hh"
+
+namespace locale {
+
+void ef__simulate__library__with__locale() {
+  setlocale(LC_ALL,"sv_SE.utf8");
+}
+  
+}
diff --git a/regression_test/locale/locale.cfg b/regression_test/locale/locale.cfg
new file mode 100644
index 0000000000000000000000000000000000000000..664ae04d8a7efba7de377f41a5f6743586af8f57
--- /dev/null
+++ b/regression_test/locale/locale.cfg
@@ -0,0 +1,20 @@
+###############################################################################
+# Copyright (c) 2000-2019 Ericsson Telecom AB
+# All rights reserved. This program and the accompanying materials
+# are made available under the terms of the Eclipse Public License v2.0
+# which accompanies this distribution, and is available at
+# https://www.eclipse.org/org/documents/epl-2.0/EPL-2.0.html
+#
+# Contributors:
+#   Baranyi, Botond
+#
+###############################################################################
+[LOGGING]
+FileMask := TTCN_ERROR | TTCN_TESTCASE | TTCN_STATISTICS | TTCN_VERDICTOP |USER
+ConsoleMask := TTCN_ERROR | TTCN_TESTCASE | TTCN_STATISTICS | TTCN_VERDICTOP | USER
+SourceInfoFormat := Stack
+LogEventTypes := Detailed
+MatchingHints := Detailed
+
+[EXECUTE]
+locale.control
diff --git a/regression_test/locale/locale.ttcn b/regression_test/locale/locale.ttcn
new file mode 100644
index 0000000000000000000000000000000000000000..c6379d8d66e7340f6875cde3793678347d6ee4f4
--- /dev/null
+++ b/regression_test/locale/locale.ttcn
@@ -0,0 +1,56 @@
+/******************************************************************************
+ * Copyright (c) 2000-2019 Ericsson Telecom AB
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/org/documents/epl-2.0/EPL-2.0.html
+ *
+ * Contributors:
+ *   Baranyi, Botond
+ *
+ ******************************************************************************/
+
+// this module contains tests for conversions and logging with certain locale settings
+// (converting to strings or logging must not be affected by locale settings)
+module locale {
+
+type component CT {}
+
+// simulates the initialization of an external
+// library, which uses a Swedish locale setting
+external function ef_simulate_library_with_locale();
+
+function f_test_float(in float val, in charstring exp) runs on CT {
+  ef_simulate_library_with_locale();
+  
+  var charstring log_res := log2str(val);
+  if (log_res != exp) {
+    setverdict(fail, "invalid log() result: ", log_res);
+  }
+  
+  var charstring conv_res := float2str(val);
+  if (conv_res != exp) {
+    setverdict(fail, "invalid flaot2str() result: ", conv_res);
+  }
+  setverdict(pass);
+}
+
+testcase tc_locale_float_zero() runs on CT {
+  f_test_float(0.0, "0.000000");
+}
+
+testcase tc_locale_float_regular() runs on CT {
+  f_test_float(1.23, "1.230000");
+}
+
+testcase tc_locale_float_exponent() runs on CT {
+  f_test_float(-123.456e78, "-1.234560e+80");
+}
+
+control {
+  execute(tc_locale_float_zero());
+  execute(tc_locale_float_regular());
+  execute(tc_locale_float_exponent());
+}
+
+}