...
    <somename>
        <description xml:lang="ia">(some ia desc)</description>
        <description xml:lang="id">(some id desc)</description>
    </somename>
...

>>> from xml.etree import ElementTree as ET
>>> 
>>> s = '''
... <somename>
...   <description xml:lang="ia">ia1 desc</description>
...   <description xml:lang="id">id1 desc</description>
...   <description xml:lang="ia">ia2 desc</description>
... </somename>
... '''
>>> 
>>> root = ET.fromstring(s)
>>> 
>>> nodes = root.findall('.//*[@{http://www.w3.org/XML/1998/namespace}lang="ia"]')
>>> print([n.text for n in nodes])
['ia1 desc', 'ia2 desc']
>>>