Senni Mattila 

What version are you using?  Latest is Trados Studio 2019 SR2 - 15.2.8.3007.

I ran a quick test with this file:

<?xml version="1.0"?>
<xliff xmlns="urn:oasis:names:tc:xliff:document:2.0" version="2.0" srcLang="en" trgLang="fr">
 <file id="someFile">
  <notes>
   <note id="n1">note for file.</note>
  </notes>
  <unit id="01_heading">
    <segment id="83D7681862266F4AA14B025CE493DC5F">
      <source>CAT tools in Europe</source>
      <target>CAT tools in Europe</target>
    </segment>				  
  </unit>
  <unit id="01_description">
    <segment id="81H7287561298D4NM16K127CE493YX1M">
      <source>The company began developing translation software in the late 1980s, and released the first Windows versions of two of the suite's major components in the early 1990s – MultiTerm in 1992, and Translator's Workbench in 1994.</source>
      <target>The company began developing translation software in the late 1980s, and released the first Windows versions of two of the suite's major components in the early 1990s – MultiTerm in 1992, and Translator's Workbench in 1994.</target>
    </segment>				  
  </unit>
 </file>
</xliff>

Saved the target after confirming the targets and get this:

<?xml version="1.0" encoding="utf-8"?>
<xliff srcLang="en" trgLang="fr-FR" version="2.0" xmlns="urn:oasis:names:tc:xliff:document:2.0">
  <file id="someFile">
    <notes>
      <note id="n1">note for file.</note>
    </notes>
    <unit id="01_heading">
      <segment state="translated" id="83D7681862266F4AA14B025CE493DC5F">
        <source>CAT tools in Europe</source>
        <target>CAT tools in Europe</target>
      </segment>
    </unit>
    <unit id="01_description">
      <segment state="translated" id="81H7287561298D4NM16K127CE493YX1M">
        <source>The company began developing translation software in the late 1980s, and released the first Windows versions of two of the suite's major components in the early 1990s – MultiTerm in 1992, and Translator's Workbench in 1994.</source>
        <target>The company began developing translation software in the late 1980s, and released the first Windows versions of two of the suite's major components in the early 1990s – MultiTerm in 1992, and Translator's Workbench in 1994.</target>
      </segment>
    </unit>
  </file>
</xliff>

I just used default settings.