How change the streets names language?

Most straightforward option is to use toolserver's locale-specific maps which shows the english labels if available (just edit the link if you want a different language). Of course this only works if the object has a "name:en" tag; otherwise the local-language "name" tag will be used.

1. As far as I know there is no web service that is displaying exclusively the name:en objects with a direct feature to process a PDF export.
2. If you need this map as PDF very urgent and someone should do that for you, have a look at Commercial_OSM_Software_and_Services
3. You can also try it on your own. Have a look at e.g. Maperitive ... There you can render your own maps and modify the style files that are quite similar to the main OSM site. You should modify the rendering rules to display name:en

If you only need a map for a smaller area, then MapOSMatic http://www.maposmatic.org/ seems to do what you want.

I always put and encourage the English names to be used in "name", if a tag is in a non English speaking country, add the local name with the local language tag. This is tricky though, some English names aren't appropriate if a place has no English name but Welsh locations should be in English for example.

eg SHEFFIELD:

name=Sheffield

name:fa=شفیلد

name:ja=シェフィールド

Amongst many others. That means the default English interface OSM always shows in English but with http://toolserver.org/~osm/locale/en.html can show the local name when the local language is selected.

I wouldn't advise changing the name of Lyon which in American is spelt with an S at the end.