Länsi-Suomen lääni is the Administrative District of Western Finland. The name of the region is Länsi-Suomi. (-en is a genetive suffix)
All of these new administrative districts (lääni) are quite artificial, and this one is especially artificial. Länsi-Suomen lääni is just an arbitrary piece of Finland for getting a big enough district for elections. It makes no sense to say "from the province of Western Finland". Major cities are Tampere, Turku and Vaasa. Other cities include Jyväskylä, Kokkola, Nokia, Pietarsaari, Pori, Rauma, Salo, Seinäjoki, Uusikaarlepyy and Uusikaupunki. If you know something about Finland, you see directly from that list how heterogeneous the area is.
The original "tribes" - with their distinct dialects - of Finns which live in this area are the Ostrobothnians and the "tribes" of Varsinais-Suomi and Häme. There are some people from Savo in Ähtäri also. This means there are two languages (Finnish and Swedish) and four Finnish dialects and cultures in one "district". The central city for Ostrobothnians is Vaasa, for Varsinais-Suomi it is Turku and for the Häme it is Tampere. Those dialects can be divide in sub-dialects of the provinces.
There are 7 provinces (maakunta) and 205 municipalities in this district. The provinces are coastal Pohjanmaa, Keski-Pohjanmaa, Etelä-Pohjanmaa, Keski-Suomi, Pirkanmaa, Satakunta and Varsinais-Suomi. The people from Varsinais-Suomi consider the Swedish-speaking a small ignorable minority, whereas 51% of Pohjanmaa speak Swedish. Tampere and Turku make jokes of each other. I know nothing about Jyväskylä. Etc. What has a potato farmer from Keski-Pohjanmaa to do with a factory worker in Uusikaupunki? They're both Finns, but what is "länsisuomalainen"?
Source: Administration of Western Finland (Ministry of Interior)