It might mean so given a certain context, bur for all intents and purposes let's just stick to to express.
The famous Vortaro Dictionary defines it as to show one's thoughts or feelings using speech, gestures or other audible or visible signs
Mi povas esprimi min mem facile en Esperanto - I can easily express myself in Esperanto.
I would use ekparolu to mean speak up!
Is there a reason 'mem' isn't used in this sentence? Not sure if there's an error to report, or if I'm just not understanding reflexive construction.
I only use "mem" when it comes to sentences where I need to make it clearer or somehow it can be misunderstood. In this case "Esprimu vin mem bone" would be to make the sentence stronger.
eg: Mi povas fari tion - i can do that Mi mem povas fari tion - i can do that myself