Use Number constructor for number conversion. Use existing noConversionRateAvailable message

app/_locales/en/messages.json

@@ -581,9 +581,6 @@
   "noAddressForName": {
     "message": "No address has been set for this name."
   },
-  "noConversionRate": {
-    "message": "No Conversion Rate"
-  },
   "noDeposits": {
     "message": "No deposits received"
   },

ui/app/components/pages/confirm-token-transaction-base/confirm-token-transaction-base.component.js

@@ -39,7 +39,7 @@ export default class ConfirmTokenTransactionBase extends Component {
     const { currentCurrency, contractExchangeRate } = this.props
 
     if (typeof contractExchangeRate === 'undefined') {
-      return this.context.t('noConversionRate')
+      return this.context.t('noConversionRateAvailable')
     } else {
       const fiatTransactionAmount = this.getFiatTransactionAmount()
       return formatCurrency(fiatTransactionAmount, currentCurrency)

ui/app/selectors/confirm-transaction.js

@@ -105,7 +105,7 @@ export const tokenAmountAndToAddressSelector = createSelector(
       const toParam = params.find(param => param.name === TOKEN_PARAM_TO)
       const valueParam = params.find(param => param.name === TOKEN_PARAM_VALUE)
       toAddress = toParam ? toParam.value : params[0].value
-      tokenAmount = valueParam ? +valueParam.value : +params[1].value
+      tokenAmount = valueParam ? Number(valueParam.value) : Number(params[1].value)
     }
 
     return {
@@ -123,7 +123,7 @@ export const approveTokenAmountAndToAddressSelector = createSelector(
 
     if (params && params.length) {
       toAddress = params.find(param => param.name === TOKEN_PARAM_SPENDER).value
-      tokenAmount = +params.find(param => param.name === TOKEN_PARAM_VALUE).value
+      tokenAmount = Number(params.find(param => param.name === TOKEN_PARAM_VALUE).value)
     }
 
     return {
@@ -142,7 +142,7 @@ export const sendTokenTokenAmountAndToAddressSelector = createSelector(
 
     if (params && params.length) {
       toAddress = params.find(param => param.name === TOKEN_PARAM_TO).value
-      tokenAmount = +params.find(param => param.name === TOKEN_PARAM_VALUE).value
+      tokenAmount = Number(params.find(param => param.name === TOKEN_PARAM_VALUE).value)
 
       if (tokenDecimals) {
         tokenAmount = calcTokenAmount(tokenAmount, tokenDecimals)