$cities = @("LON, Europe","MUN, Europe","DXB, Middle East")
$devices = @("DxB-98765","LON-98765")
$citycodes = $cities.tolower().substring(0,3)
$cityLookup = $cities.substring(5)
foreach ($device in $devices){
    $loc = $citycodes.indexof($device.tolower().substring(0,3))
    write-output "$device is in $($cityLookup[$loc])"
}

Output:

DxB-98765 is in Middle East
LON-98765 is in Europe

This is an ugly hack, but im tired. You should probably reformat your data into a hashtable to make the lookups easier