Yes, the language matters and the court may dismiss your eviction case on procedural grounds–no matter how deserving on the merits–if the language is wrong.
Some documents, such as the 14-day notice, must be in the exact verbiage required by statute. In some local jurisdictions additional specific language must be in the notice and/or additional documents must be served with it.
There are some multi-state websites that show up in Google results with form generators that create notice forms that will not hold up in Washington courts. We do not post forms for every situation or jurisdiction because the new laws vary and are not simple to implement. Consult with an attorney before serving documents.