fix error's raw log messages ugly encoding

Closes: #5785

CHANGELOG.md

@@ -44,6 +44,9 @@ balances or a single balance by denom when the `denom` query parameter is presen
 * (client) [\#5640](https://github.com/cosmos/cosmos-sdk/pull/5640) The rest server endpoint `/swagger-ui/` is replaced by ´/´.
 * (x/auth) [\#5702](https://github.com/cosmos/cosmos-sdk/pull/5702) The `x/auth` querier route has changed from `"acc"` to `"auth"`.
 * (store/types) [\#5730](https://github.com/cosmos/cosmos-sdk/pull/5730) store.types.Cp() is removed in favour of types.CopyBytes().
+* [\#5785](https://github.com/cosmos/cosmos-sdk/issues/5785) JSON strings coerced to valid UTF-8 bytes at JSON marshalling time
+are now replaced by human-readable expressions. This change can potentially break compatibility with all those client side tools
+that parse log messages.
 
 ### API Breaking Changes
 

x/bank/keeper/keeper.go

@@ -67,7 +67,7 @@ func (k BaseKeeper) DelegateCoins(ctx sdk.Context, delegatorAddr, moduleAccAddr
 		balance := k.GetBalance(ctx, delegatorAddr, coin.Denom)
 		if balance.IsLT(coin) {
 			return sdkerrors.Wrapf(
-				sdkerrors.ErrInsufficientFunds, "failed to delegate; %s < %s", balance, amt,
+				sdkerrors.ErrInsufficientFunds, "failed to delegate; %s is smaller than %s", balance, amt,
 			)
 		}
 
@@ -265,7 +265,7 @@ func (k BaseSendKeeper) SubtractCoins(ctx sdk.Context, addr sdk.AccAddress, amt
 
 		_, hasNeg := sdk.Coins{spendable}.SafeSub(sdk.Coins{coin})
 		if hasNeg {
-			return nil, sdkerrors.Wrapf(sdkerrors.ErrInsufficientFunds, "%s < %s", spendable, coin)
+			return nil, sdkerrors.Wrapf(sdkerrors.ErrInsufficientFunds, "%s is smaller than %s", spendable, coin)
 		}
 
 		newBalance := balance.Sub(coin)