Changed the wording from "from 0 to maximum available" to "from 2 to maximum available".
May I also suggest putting in a number rather than "maximum available" and also clarifying that mixin = 0 is still allowed if the user has unmixable outputs (dust), which he wants to "undust" using sweep_unmixable (comment from dEBRUYNE-1 ).
m_cmd_binder.set_handler("incoming_transfers",boost::bind(&simple_wallet::show_incoming_transfers,this,_1),tr("incoming_transfers [available|unavailable] - Show incoming transfers, all or filtered by availability"));
m_cmd_binder.set_handler("payments",boost::bind(&simple_wallet::show_payments,this,_1),tr("payments <PID_1> [<PID_2> ... <PID_N>] - Show payments for given payment ID[s]"));
m_cmd_binder.set_handler("transfer_original",boost::bind(&simple_wallet::transfer,this,_1),tr("transfer [<mixin_count>] <addr_1> <amount_1> [<addr_2> <amount_2> ... <addr_N> <amount_N>] [payment_id] - Transfer <amount_1>,... <amount_N> to <address_1>,... <address_N>, respectively. <mixin_count> is the number of extra inputs to include for untraceability (from 0 to maximum available)"));
m_cmd_binder.set_handler("transfer_original",boost::bind(&simple_wallet::transfer,this,_1),tr("transfer [<mixin_count>] <addr_1> <amount_1> [<addr_2> <amount_2> ... <addr_N> <amount_N>] [payment_id] - Transfer <amount_1>,... <amount_N> to <address_1>,... <address_N>, respectively. <mixin_count> is the number of extra inputs to include for untraceability (from 2 to maximum available)"));
m_cmd_binder.set_handler("transfer",boost::bind(&simple_wallet::transfer_new,this,_1),tr("Same as transfer_original, but using a new transaction building algorithm"));
m_cmd_binder.set_handler("sweep_unmixable",boost::bind(&simple_wallet::sweep_unmixable,this,_1),tr("Send all unmixable outputs to yourself with mixin 0"));
m_cmd_binder.set_handler("sweep_all",boost::bind(&simple_wallet::sweep_all,this,_1),tr("Send all unlocked balance an address"));